reference
238 pages in this category.
ccusage
Local-first CLI and TypeScript library that reads JSONL session logs from Claude Code, Codex, and 13 other coding agents to produce daily/weekly/monthly/session/billing-block reports of token spend.
az
Cross-platform command-line interface for managing Azure resources, running ARM-based and data-plane operations from a terminal or pipeline.
wrangler
Package-level reference for the wrangler CLI on npm — install, Node support, transitive dependency footprint, and platform-binding gotchas.
winston
Package-level reference for winston on npm — transports, formats, levels, daily rotation, and production patterns.
vue (@vue/cli)
The legacy @vue/cli command-line tool for scaffolding and serving Vue projects — deprecated in favour of create-vue + Vite, retained as reference for existing apps.
vue
Package-level reference for Vue 3 — Composition API, reactivity, single-file components, the Vue 2 → 3 migration, and the broader ecosystem (Pinia, Vue Router, Nuxt).
vercel
Vercel's official CLI for deploying frontend apps, managing environments, syncing env vars, tailing logs, and rolling back via alias re-pointing.
vercel
Package-level reference for the vercel CLI on npm — install, Node support, command surface, project linking model, and where it fits next to wrangler / netlify-cli.
valibot
Package-level reference for valibot — schemas, transforms, pipes, branding, safeParse, and the tree-shaking advantage over zod.
type-fest
Package-level reference for type-fest on npm — install (dev-only, pure types), TS version requirements, recursion limits, and alternatives.
redis
Package-level reference for node-redis on npm — pipelining, pub/sub, TTL, the v3-to-v4 API rewrite, and rate-limit patterns.
react-dom
Package-level reference for react-dom — client/server rendering, hydration, portals, flushSync, and the React 19 root API.
react
Package-level reference for the React library on npm — install, paired react-dom, server-component model, and upgrade gotchas.
pino
Package-level reference for pino on npm — child loggers, redaction, transports, serializers, and migration notes.
pg
Package-level reference for node-postgres on npm — pools, parameterized queries, transactions, LISTEN/NOTIFY, and COPY streaming.
npm-check-updates
Package-level reference for npm-check-updates on npm — install, Node support, the ncu binary, doctor mode, workspaces, and where it fits next to npm outdated, taze, and bun update.
next
Package-level reference for Next.js — App Router, server components, server actions, middleware, caching, and the 14 → 15 → 16 migration path.
ncu
The ncu CLI from npm-check-updates rewrites package.json to bump dependency versions — interactive mode, filters, doctor rollback, and workspaces support.
mysql2
Package-level reference for mysql2 on npm — promise API, prepared statements, pooling, streaming, and migration from mysql.
mongoose
Package-level reference for mongoose on npm — schemas, models, transactions, populate, indexes, and 7-to-8 migration.
ioredis
Package-level reference for ioredis on npm — cluster, sentinel, pipelining, Lua scripts via defineCommand, and stability characteristics.
hono
Package-level reference for Hono — minimal routing, typed handlers, middleware, RPC client, and deployment to Cloudflare Workers, Bun, Deno, Node, and Vercel Edge.
fastify
Package-level reference for the Fastify framework on npm — install, plugin model, Node support, and validation/encapsulation gotchas.
express
Package-level reference for Express on npm — install, middleware model, Node support, 4-to-5 migration, and production deployment.
elysia
Package-level reference for Elysia — end-to-end type safety, plugins, Eden RPC client, schema validation, and Bun-first deployment.
effect
Package-level reference for the Effect library — Effect values, generators, fibers, error channels, dependency injection, and the 2.x → 3.x migration.
drizzle-orm
Package-level reference for Drizzle ORM — schema definitions, type-safe queries, relations, migrations with drizzle-kit, and deployment patterns.
dotenv
Package-level reference for the dotenv config loader on npm — install, native Node alternatives, dotenvx successor, and gotchas.
diff2html-cli
Package-level reference for the diff2html-cli renderer on npm — install, runtime support, peer-deps, and alternatives.
dayjs
Package-level reference for the Day.js date library on npm — install, plugin model, version policy, and alternatives.
cors
Package-level reference for cors on npm — preflight handling, credentialed requests, dynamic origins, and Express integration.
commander
Package-level reference for the commander CLI framework on npm — install, version policy, TypeScript extras, and alternatives.
chalk
Package-level reference for the chalk ANSI-styling library on npm — install, ESM-only policy, peer-deps, and alternatives.
body-parser
Package-level reference for body-parser on npm — JSON, urlencoded, raw and text middleware, webhook signatures, and Express 4.16+ bundling.
axios
Package-level reference for axios — interceptors, request configuration, error handling, and the migration story from 0.x to 1.x.
astro
Package-level reference for the Astro framework on npm — install, integration ecosystem, runtime support, and SSR/SSG adapter gotchas.
ai
Package-level reference for the Vercel AI SDK — streamText, generateObject, tool calling, structured output, and the multi-provider model interface.
@vue/cli
Reference for the legacy @vue/cli npm package — install, command surface, plugin model, and why create-vue + Vite is the recommended path for new projects.
Zowe CLI
Open-source command-line bridge into z/OS — manage datasets, jobs, USS files, consoles, TSO, and Db2 from Mac/Linux/Windows over z/OSMF or RSE-API.
z/OS TCP/IP
Drive the z/OS Communications Server TCP/IP stack — NETSTAT variants, PING, TRACERTE, RESOLVE, PROFILE.TCPIP configuration, OMPROUTE, and SSH from z/OS UNIX, with end-to-end troubleshooting recipes.
z/OS FTP Reference
FTP from TSO, batch FTP via JCL, SITE parameters, transfer modes, FTPS, FTP.DATA configuration, and JES spool transfers.
xcopy
Copy files and directory trees with attribute preservation, date filtering, exclusion lists, and verification. The step between copy and robocopy for most scripting needs.
xattr
Deep-dive on macOS extended attributes — listing, reading, writing, and removing xattrs with xattr(1); the Gatekeeper com.apple.quarantine flag; Spotlight metadata attributes; ACLs via ls -le and chmod +a; preserving attributes on copy with cp -p and rsync -X.
wsl
Install, list, export, import, configure, and clone WSL distributions using the wsl.exe command on Windows 10 and 11.
wmic
Query and manage Windows system information — hardware, software, processes, services, and more — from the command prompt using WMI classes and WMIC's SQL-like syntax.
Windows Terminal
Configure Windows Terminal — settings.json structure, profiles for pwsh/cmd/wsl/ssh, keybindings, colour schemes, panes, and the wt.exe CLI.
whoami
Display the current user name, SID, group memberships, and privileges from the Windows command prompt — essential for auditing security context in scripts and support scenarios.
wevtutil
Query, export, clear, and manage Windows Event Log channels from the command line — the primary CLI for event log automation, log archiving, and scripted log analysis on Windows.
USS
The UNIX side of z/OS — OMVS, ISHELL, oedit, BPXBATCH, file tagging, zFS, and bridging shell scripts to MVS batch.
tzutil & w32tm
Read and set the system timezone with tzutil, then query, configure, and force-sync the Windows Time service with w32tm — including NTP peer configuration and Kerberos-clock-drift recovery.
TSO/ISPF Navigation
Complete ISPF menu options, primary commands, line commands, edit profile, utilities, DSLIST, SDSF, TSO commands, RACF, and keyboard shortcuts.
tracert
Trace the sequence of routers between your machine and a destination by sending probes with increasing TTL values — the go-to tool for locating where a network path breaks or introduces high latency.
tmutil
Drive Time Machine backups, destinations, exclusions, local APFS snapshots, restores, and verification entirely from the terminal — without opening System Settings.
timeout
Pause a batch script for a specified number of seconds with an optional keypress bypass — a reliable replacement for the ping-delay idiom and a safer alternative to sleep in Windows CMD scripts.
tasklist
Display all running processes on a local or remote Windows machine with PID, memory usage, session, and optional service or module details — the cmd.exe equivalent of Task Manager for scripts.
taskkill
End one or more running Windows processes by PID or image name from the command prompt, with options for force termination, process tree killing, filtering, and remote targets.
takeown
Transfer ownership of files and directories to the current user or the Administrators group from an elevated command prompt — a prerequisite for modifying ACLs on system-protected paths.
systeminfo
Display detailed OS, hardware, and network configuration for the local or a remote Windows machine. Covers output formats, remote querying, filtering, and parsing in scripts.
system_profiler
Deep-dive on system_profiler(8) — macOS's built-in inventory tool. Covers data types, text/XML/JSON output, piping into jq and plutil, common SP* probes (hardware, displays, memory, storage, USB, network, software), detail levels, and fleet inventory recipes.
Sysinternals
Bootstrap and drive the headless Sysinternals utilities — PsExec, Handle, PsList, Autoruns, ProcMon, ListDLLs — for process spelunking, file-lock hunting, autostart auditing and scripted system tracing on Windows.
ssh
Connect to remote hosts, transfer files, and forward ports over an encrypted channel using the OpenSSH client built into Windows 10 and later.
softwareupdate
Deep-dive on softwareupdate(8), Apple's CLI for macOS system updates — listing pending updates, installing recommended-only or specific items, scheduling, ignoring updates, installing Rosetta and Command Line Tools, and pairing with mas and brew for full system update automation.
shutdown
Initiate, schedule, abort, or force a shutdown, restart, logoff, hibernate, or sleep on a local or remote Windows machine from the command line — essential for scripted maintenance, patch automation, and remote administration.
set
Set, display, and delete cmd.exe environment variables within the current session, perform integer arithmetic with /A, and read interactive user input with /P.
SDSF
Browse, filter, and act on JES2 spool from inside ISPF — find your job, read SYSOUT, cancel, purge, and issue operator commands.
Scoop
Install dev tools without admin rights using Scoop — buckets, manifests, multi-version installs, and reproducible setups.
schtasks
Create, query, run, end, and delete scheduled tasks on local or remote Windows machines from the command prompt — the scripting interface to Windows Task Scheduler.
sc
Query, create, configure, start, stop, and delete Windows services from the command line — the scripting interface to the Service Control Manager, equivalent to the Services MMC snap-in but fully automatable.
runas
Launch a program in the security context of a different user account — elevate to Administrator, switch to a service account, or test application behaviour under a restricted identity.
route
Display, add, delete, and modify entries in the Windows IP routing table — control how packets are forwarded between subnets, add persistent static routes, and diagnose routing failures.
robocopy
Production-grade file and directory synchronisation with mirroring, multi-threading, retry logic, logging, and exclusion filters. The go-to for backup scripts and deployment pipelines on Windows.
rmdir / rd
Delete empty or entire directory trees from the Windows command prompt. Covers the /S and /Q flags, force-removing read-only trees, and safe deletion patterns.
reg
Query, add, modify, export, and import Windows registry keys and values with the built-in reg.exe — the scriptable, no-dependency tool for everything from one-off tweaks to full backup-and-restore.
RACF
TSO commands for RACF user, group, dataset, and general-resource profile administration on z/OS.
PowerShell Scripting
Author production-grade PowerShell: advanced functions with [CmdletBinding()], parameter validation, pipeline-bound parameters, splatting, switch parameters, .ps1 vs .psm1, and all the control-flow constructs.
PowerShell Remoting
Execute PowerShell against one or many remote hosts using WinRM or SSH transport, persistent sessions, credential management, and JEA.
PowerShell Pipelines
Deep dive on PowerShell's object pipeline: Where-Object, Select-Object, ForEach-Object, Sort-Object, Group-Object, Measure-Object, Compare-Object, Out-GridView, parallel execution, and the two filter forms.
PowerShell Modules
Install, discover, update, and author PowerShell modules: PowerShellGet, PSResourceGet, the Gallery, $PSModulePath, $PROFILE customisation, PSReadLine, SecretManagement, and the must-have module shortlist.
PowerShell Error Handling
Master terminating vs non-terminating errors, $ErrorActionPreference, try/catch/finally, throw vs Write-Error, transcripts, and strict mode.
PowerShell Built-in Variables
Complete reference for every automatic and preference variable built into PowerShell — $_, $Error, $MyInvocation, $PSCmdlet, $Host, $PSVersionTable, $ExecutionContext, and all preference variables that tune runtime behaviour.
powercfg
Manage Windows power plans, enable or disable hibernation, diagnose battery health and sleep failures, and generate energy efficiency reports from the command prompt.
pmset
Inspect and configure sleep, wake, hibernate, and battery behaviour on macOS. Covers per-source profiles, scheduled wake, sleep-prevention diagnostics, battery reports, and hibernate modes.
ping
Send ICMP echo requests to a host to test reachability, measure round-trip latency, and detect packet loss from the Windows command prompt.
pbcopy & pbpaste
Pipe data into and out of the macOS pasteboard from the shell — multi-pasteboard targets, newline handling, shell aliases, and real-world copy-paste recipes.
pathping
Trace the route to a destination and measure per-hop packet loss and latency over a sustained sampling period — more diagnostic than tracert and more thorough than ping for identifying intermittent network problems.
osascript
Drive macOS GUI apps, system events, dialogs, notifications, and Finder from the terminal using AppleScript or JavaScript for Automation (JXA).
nslookup
Query DNS servers for A, AAAA, MX, TXT, NS, PTR, and other resource records from the Windows command prompt — the built-in tool for diagnosing name resolution issues.
networksetup
Script every aspect of macOS network configuration — Wi-Fi joining, DNS servers, proxies, locations, and service order — from a single first-party command-line tool.
netstat
Display active TCP/UDP connections, listening ports, routing tables, interface statistics, and per-connection process IDs from the Windows command prompt.
netsh
Configure network interfaces, firewall rules, wireless profiles, port proxies, and Winsock settings from an elevated command prompt — the comprehensive Windows network configuration CLI.
net user
Create, modify, delete, and list local Windows user accounts from the command prompt — set passwords, manage account expiry, lock/unlock accounts, and control logon hours.
net localgroup
Create, delete, and modify local security groups on a Windows machine — add or remove members, list group memberships, and manage built-in groups from the command prompt.
nano
GNU's small, on-screen-hinted terminal text editor — the default modal-free alternative to vi/emacs that you can drive without ever learning a command vocabulary.
move
Move files to a new location or rename them within the Windows command prompt. Covers single files, wildcards, directory renames, overwrite control, and cross-drive behaviour.
mountvol
List, create, and remove NTFS volume mount points and display the unique volume GUID path for any drive letter or directory junction from the command prompt.
mkdir / md
Create one or more directories from the Windows command prompt. Covers single and nested directory creation, batch patterns, and common scripting idioms.
mdfind
Query macOS's Spotlight index from the shell — fast name, content, and metadata search across the whole filesystem, with scope, attributes, and live-update modes.
logman
Create, start, stop, and manage Data Collector Sets for performance counters, event traces, and configuration data — the command-line interface to Windows Performance Monitor for scripted monitoring and automated log collection.
launchctl
Bootstrap, bootout, kickstart, print, and enable/disable services with launchctl on macOS: agents vs daemons, plist anatomy, user/system domains, RunAtLoad vs KeepAlive vs StartInterval vs StartCalendarInterval, and recipes for periodic scripts and on-demand workers.
JES2
z/OS Job Entry Subsystem 2 operator slash-commands for jobs, initiators, output, classes, NJE, and spool — from the console and from SDSF.
JCL Quick Reference
Job Control Language syntax, common statements, EXEC, DD, and SYSOUT patterns.
JCL DD Statement
Comprehensive reference for the JCL DD statement: DSN, DISP, DCB, SPACE, UNIT, VOL=SER, concatenation, DUMMY, SYSOUT, KEYLEN.
ISPF Edit
Deep dive into the ISPF editor — primary commands, line commands, BNDS/CC/MM column edits, ISREDIT macro services, profile management, and recovery.
ipconfig
Display and manage TCP/IP network configuration for all adapters on a Windows machine — covers full adapter details, DNS cache operations, and DHCP lease management.
IEBCOPY
IBM utility for copying, merging, compressing, unloading, and reloading PDS and PDSE libraries on z/OS, including member selection, rename, and exclusion.
IDCAMS
Define, copy, list, alter, and delete VSAM clusters and general datasets — the everyday utility for catalog and dataset lifecycle on z/OS.
icacls
Display and modify NTFS access control lists on files and directories — grant, deny, or remove permissions for users and groups, manage inheritance, and save or restore full ACL sets.
hostname
Display the DNS hostname of the local Windows machine from the command prompt — useful in scripts to identify the machine without parsing systeminfo output.
Homebrew
Install, search, upgrade, pin, tap, bottle, and bundle packages with Homebrew on macOS: formulae vs casks, brew services, Brewfile-driven machine bootstrap, Apple-Silicon vs Intel prefixes, brew doctor, brew cleanup, and recovery recipes.
gpresult & gpupdate
Inspect the Resultant Set of Policy that applied to a user and computer with gpresult, then force a refresh with gpupdate — including HTML reports, scope filtering, and the classic 'why didn't my GPO take effect?' workflow.
getmac
Display the MAC (hardware) addresses and associated transport names for all network adapters on a local or remote Windows machine — useful for asset inventory, DHCP reservation setup, and network access control.
GDG
Define, reference, and clean up z/OS generation data groups via IDCAMS — relative generations, rollover behaviour, model DSCBs, and the modern GDGEXTENDED mode.
fsutil
Inspect and manage NTFS file system internals — query volume info, manage hard links, sparse files, reparse points, the USN journal, and the dirty bit — from an elevated command prompt.
findstr
Search for string patterns inside files or piped input on Windows — the built-in grep equivalent for cmd.exe, with support for regular expressions, case-insensitive matching, and recursive directory searches.
fc
Compare two text or binary files line-by-line or byte-by-byte and report their differences — the built-in Windows equivalent of Unix diff for quick file audits in cmd.exe.
echo
Print text to stdout, expand environment variables, write blank lines, redirect output to files, and toggle command-echoing in cmd.exe batch scripts.
duti
Drive macOS Launch Services from the command line — assign default apps for UTIs, file extensions, and URL schemes; understand the viewer/editor/all/shell/none roles; bulk-load file associations from a settings file; rebuild the Launch Services database when changes refuse to stick.
driverquery
Display all installed device drivers on a local or remote Windows machine — module name, type, link date, and driver file path — for hardware audits and troubleshooting.
dism
Service Windows images and the running OS — enable/disable optional features, repair the component store, mount and edit WIM/ESD images, add drivers, and manage editions from an elevated command prompt.
diskutil
Command-line front-end to Disk Utility on macOS — list, partition, format, repair, encrypt, and snapshot APFS containers, plus build and tear down software RAID volumes.
diskpart
Create, delete, format, extend, shrink, and assign drive letters to disk partitions from the Windows command prompt using an interactive or scripted REPL interface.
dir
Display files and folders in a directory with filtering, sorting, formatting, and recursive traversal options. The Windows cmd.exe equivalent of Unix ls.
DFSORT
IBM DFSORT control statements and ICETOOL operators for sorting, merging, joining, and reshaping batch datasets on z/OS.
DFSMShsm
Migrate, recall, back up, and recover datasets across ML0/ML1/ML2 tiers with TSO H-commands and ARC operator commands; bulk-recall recipes, recall timing, and audit messages.
del
Delete one or more files from the Windows command prompt. Covers wildcards, quiet mode, attribute overrides, recursive deletion patterns, and the distinction from rmdir.
defrag
Analyze, defragment, and optimize volumes from the command line — consolidate free space on HDDs, issue TRIM on SSDs, and schedule or review optimization tasks.
defaults
Read, write, search, and delete macOS preference plists with the `defaults` CLI: data types, domains, current-host scope, the killall dance, finding undocumented keys via plist diffing, and a curated bootstrap recipe.
Db2 SPUFI
Run SQL through SPUFI, drive Db2 with DSN subsystem commands, BIND packages and plans, schedule DSNTEP2 in JCL, query the SYSIBM catalog, and generate DCLGEN.
copy
Copy one or more files to a new location in the Windows command prompt. Covers single-file copy, wildcard batches, file concatenation, and binary vs ASCII modes.
codesign
End-to-end macOS distribution pipeline — sign binaries and app bundles with codesign, notarize with notarytool, staple tickets with stapler, and verify Gatekeeper acceptance with spctl.
cls
Clear all text from the cmd.exe or PowerShell console window and reset the cursor to the top-left — the single command for resetting a terminal session's visible output.
CICS CEMT
Drive the CICS Master Terminal transaction — INQUIRE, SET, and PERFORM verbs for programs, tasks, files, connections, and region-level operations like NEWCOPY refresh and SNAP dumps.
Chocolatey
Install, upgrade, pin, and script software installs on Windows with the choco CLI, packages.config files, and custom sources.
chkdsk
Scan a FAT or NTFS volume for file system errors and bad sectors, optionally repairing them — the built-in Windows disk health and integrity tool for drives and volumes.
certutil
The dual-purpose Windows CLI for certificate-store management and as the most reliable built-in tool for file hashing, base64 encoding, and CRL/CTL handling — no install required.
cd
Navigate the Windows command prompt's current working directory. Covers drive switching, absolute and relative paths, UNC paths, and path-with-spaces quoting.
caffeinate
Prevent display, idle, system, or user-active sleep for the duration of a command, a fixed time, or a process — without permanently changing pmset.
bcdedit
View and modify the Windows Boot Configuration Data store — manage boot entries, set default OS, change timeouts, enable debugging, and configure boot options from an elevated command prompt.
attrib
View and modify Windows file attributes (hidden, read-only, system, archive) from the command line. Covers all attribute flags, recursive operations, and practical recipes for unhiding malware-hidden files and managing backups.
arp
Display, add, and delete entries in the Windows ARP (Address Resolution Protocol) cache — map IP addresses to MAC addresses, detect IP conflicts, and diagnose Layer 2 connectivity issues.
Zod
TypeScript-first runtime validation library. Define schemas, validate inputs, infer static types — works at API boundaries, env config, forms, and tRPC.
vim
Bram Moolenaar's modal editor. Covers modes, verb-noun grammar, text objects, registers, marks, windows, search-and-replace, quickfix, macros, configuration, and a high-value baseline .vimrc.
typing
Go beyond list[int] and str | None. Covers Protocol, TypeVar bounds, ParamSpec, Concatenate, Self, Annotated, TypedDict with NotRequired/Required, TypeAlias, TypeGuard, TypeIs, cast, assert_type, and reveal_type.
TypeScript Project References
Split a TypeScript codebase into composite sub-projects, build them incrementally in dependency order with tsc --build, and integrate the result with bundlers, Turborepo, and Nx.
TypeScript Modules
Deep dive into TypeScript's module system — module/moduleResolution pairs, .mts/.cts file extensions, NodeNext vs Bundler resolution, paths, and tsconfig extends.
TypeScript Compiler API
Drive the TypeScript compiler programmatically — parse SourceFiles, query the type checker, transform ASTs with the factory, and write codemods that scale across a monorepo.
typeof & keyof
TypeScript's typeof promotes a runtime value into the type position; keyof extracts the union of property keys. Together they form the backbone of type-safe lookups, enum-from-object patterns, and inferred shapes.
type-fest
Sindre Sorhus's collection of essential TypeScript utility types — PartialDeep, ReadonlyDeep, SetOptional, RequireAtLeastOne, Merge, Tagged, JsonValue, Opaque, and dozens more — so you don't hand-roll them.
ts-node, tsx & Friends
Compare ts-node, tsx, Node 22.6+ --experimental-strip-types, Bun, and Deno for running .ts files directly; pick the right tool, configure watch mode, and avoid the classic ESM / type-strip pitfalls.
tmux
Run multiple persistent terminal sessions, windows, and panes inside one shell. Covers the session/window/pane mental model, default keybindings, copy-mode, and a minimal tmux.conf.
Testing Strategies
A practical guide to test design — the pyramid (unit/integration/e2e), fixture and mock patterns, property-based testing, snapshot tests, and CI strategies that scale.
Template Literal Types
Template literal types let TypeScript pattern-match and synthesize string types — covering Uppercase/Lowercase intrinsics, infer-based parsers (Split, Join, CamelCase), route-param extraction, JSON path keys, and typed i18n helpers.
tar
Bundle directory trees into a single archive file with optional compression. Covers create/extract/list, gzip/bzip2/xz formats, exclusions, transforms, and incremental backups.
subprocess
Run external commands from Python with subprocess. Covers run vs Popen, capture_output, streaming, pipes, timeouts, env/cwd overrides, and shlex quoting safety.
Structured Output
Techniques for reliable structured generation — JSON mode, schema-constrained decoding, function/tool calls as output, and validator pairing with Pydantic or Zod.
Structural Typing
Understand TypeScript's structural type system — assignability is based on shape, not name; excess property checks are the one exception; nominal typing requires branded types or class privates.
streamlit
Build interactive web apps for data and ML in pure Python. Covers widgets, layout, session state, caching, multipage apps, and deployment patterns.
SOLID
A modern walk-through of the SOLID principles — single responsibility, open-closed, Liskov, interface segregation, dependency inversion — with anti-examples and refactors in TypeScript and Python.
shellcheck
Catch quoting bugs, missing checks, and POSIX portability mistakes in shell scripts. Covers every flag, severity levels, inline directives, CI/pre-commit integration, and the most common rules.
Security Fundamentals
OS-level security primitives every operator should know: users and groups, file permissions, Linux capabilities, SUID/SGID, mandatory access control (SELinux, AppArmor), sandboxing concepts, least privilege, and encryption at rest vs in transit.
scikit-learn
Build classical ML pipelines with scikit-learn. Covers the estimator API, train_test_split, Pipeline, ColumnTransformer, cross-validation, metrics, and model persistence.
satisfies Operator
TypeScript's satisfies operator checks a value against a type while preserving its narrow literal inferred type. The middle ground between an annotation that widens and an as cast that lies.
rsync
Copy and synchronise files locally or over SSH using a delta-transfer algorithm that only sends changed parts. Covers archive mode, deletion, filtering, progress, and snapshot backups.
React with TypeScript
Type-safe React patterns — function components, prop types, children, event handlers, refs, generic components, polymorphic `as` props, and Zod-powered forms.
React Basics
Foundational React patterns — function components, JSX, props, hooks (useState, useEffect, useRef, useContext), list rendering, and form handling — with TypeScript throughout.
re
Python's built-in regex module — compile vs not, match/search/findall/finditer/sub, named groups, lookarounds, verbose mode (re.X), and how it differs from PCRE.
pyproject.toml
The canonical config file for modern Python projects — [project] metadata, [build-system] backends (setuptools, hatchling, pdm-backend, poetry-core, flit-core), [tool.*] sections, dynamic versioning, scripts, building, and publishing.
Prompt Engineering Patterns
Reliable prompt structures for reasoning, extraction, classification, generation, extended thinking, and vision tasks with Claude.
Processes
Process lifecycle on Unix: fork/exec/wait, PIDs, signals, zombies and orphans, parent/child trees, process groups, sessions, controlling terminals, and a tour of Linux cgroups.
Prisma
Schema-first ORM for Node.js with auto-generated typed client, declarative migrations, relations, transactions, and seeding — for PostgreSQL, MySQL, SQLite, MongoDB, and more.
pre-commit
Run linters, formatters, and validators automatically on every git commit. Covers .pre-commit-config.yaml, essential hooks (ruff, mypy, check-yaml), autoupdate, and CI integration.
Playwright
Cross-browser end-to-end test runner from Microsoft with auto-waiting, role-based selectors, trace viewer, and codegen.
permissions
POSIX file permissions on Linux. Covers symbolic and octal chmod, ownership with chown, the meaning of r/w/x for files vs. directories, setuid/setgid/sticky bits, umask, ACLs, capabilities, and immutable attributes.
pdb
Pause, inspect, and step through Python programs with pdb. Covers breakpoint(), command reference, post-mortem debugging, conditional breakpoints, and enhanced alternatives like ipdb, pdbpp, and pudb.
PCRE
PCRE2 syntax reference — character classes, quantifiers, anchors, groups, lookarounds, backreferences, flags, and advanced features used in grep, sed, nginx, PHP, and dozens of other tools.
node:stream
Node.js streams — Readable, Writable, Duplex, and Transform, the modern pipeline() API, backpressure, async iterators, Web Streams interop, and patterns for piping files, HTTP bodies, and gzip compression.
node:fs
Node.js file system module — the three APIs (callback, sync, promises), reading and writing files, directory operations, watchers, atomic writes, and path module pairing.
Networking Stack
How packets actually move: the OSI and TCP/IP layer models, the BSD socket API, TCP vs UDP, the three-way handshake, MTU/MSS, NAT and port translation, basic IP routing, and the full DNS resolution flow.
Memory Management
How operating systems give every process its own address space: virtual memory and paging, swap, the OOM killer, mmap, copy-on-write, the page cache, allocator choices (glibc, jemalloc, mimalloc), and how to read memory counters in top, ps, and free.
logging
Configure Python's built-in logging module — loggers, handlers, formatters, dictConfig, rotation, structured records, and how it compares to loguru.
LLM Evaluations
Build production evaluation pipelines for LLM applications — golden datasets, LLM-as-judge, rubrics, statistical significance, regression detection, and evals vs tests.
json
Encode and decode JSON in Python with the stdlib json module. Covers dumps/loads, indent/sort_keys/separators, custom default= and JSONEncoder, object_hook decoding, JSONL streaming, and orjson/ujson/msgspec comparison.
itertools & functools
The two stdlib modules every Python developer pairs together — iterator algebra (chain, groupby, batched, pairwise) and function plumbing (lru_cache, partial, reduce, singledispatch, cached_property).
infer Keyword
TypeScript's infer keyword declares a fresh type variable inside a conditional type, letting you pull a sub-type out of a matched shape. It powers ReturnType, Parameters, Awaited, and most advanced type extractors.
gpg
Practical GnuPG cheat sheet — generate keys, sign and verify files, encrypt for a recipient, sign git commits and tags, and manage trust without the bureaucracy.
Filesystems
Core filesystem concepts every operator should know: inodes, directory structure, hard vs symbolic links, journaling, copy-on-write, and a head-to-head of ext4, XFS, Btrfs, ZFS, APFS, and NTFS with mount options and pitfalls.
Few-Shot Prompting
In-context learning techniques — example selection, format design, count tuning, dynamic retrieval of demonstrations, and pitfalls of few-shot prompting.
Fastify
Fastify is a high-performance Node.js web framework with schema-driven validation, plugin encapsulation, hooks, decorators, and built-in Pino logging — covering routes, plugins, hooks, error handling, and production hardening.
dotenv
Load configuration and secrets from .env files into process.env at startup, with multi-environment files, variable expansion, schema validation, and Node 20.6+ built-in --env-file alternatives.
Discriminated Unions
Discriminated unions model finite states with a shared literal tag, enabling exhaustive narrowing in switch statements, Result-style error handling, reducer actions, and pattern-matched API responses.
dig
Query DNS records of any type from any resolver — A, AAAA, MX, TXT, NS, SOA, SRV, CAA — with formatted output, reverse lookups, and full delegation tracing.
Design Patterns
A practical reference for classic OOP design patterns — Strategy, Observer, Factory, Adapter, Decorator, Repository — with examples in Python, TypeScript, and Go.
Deno
Deno is a secure, modern JavaScript and TypeScript runtime built on V8 with permission-based sandboxing, built-in TypeScript, a curated standard library on JSR, and a complete toolchain (fmt, lint, test, bench, compile).
Declaration Merging
Deep dive into TypeScript declaration merging — interface merging, namespace + class, namespace + function, module augmentation, global augmentation, and the Express Request pattern.
Day.js
Parse, format, manipulate, compare, and convert timezones for dates in JavaScript using Day.js — a 2 kB Moment-compatible alternative with a plugin-based architecture.
datetime
Work with dates, times, and timezones in Python using the stdlib datetime module and zoneinfo. Covers aware vs naive datetimes, ISO-8601 parsing, strftime/strptime, timedelta arithmetic, and DST handling.
dataclasses
Define typed data containers with @dataclass — frozen, slots, kw_only, default_factory, __post_init__, asdict, replace, and how it compares to attrs, pydantic, NamedTuple, TypedDict.
cron
Time-based job scheduler on Unix. Covers crontab syntax, user vs. system crontabs, environment quirks, logging, anacron, and the modern systemd timer alternative.
Commander.js
Build full-featured Node.js CLIs with positional arguments, typed options, subcommands, auto-generated help, lifecycle hooks, and a distributable bin in package.json.
Codex Tips & AGENTS.md
Advanced Codex CLI workflows — AGENTS.md authoring, profiles, experimental hooks, notify callbacks, non-interactive exec scripting, session resume and fork, and codex cloud.
Codex Sub-Agents & Task Delegation
How Codex CLI supports delegating to child agents — the experimental /agent system, codex exec as a sub-agent pattern, MCP-mediated agent-to-agent calls, isolation boundaries, and orchestration patterns.
Codex Slash Commands
Complete reference for every built-in Codex CLI slash command — session control, model switching, sandboxing, MCP management, and TUI utilities.
Codex MCP Servers
Add and configure Model Context Protocol (MCP) servers in Codex CLI — config.toml [mcp_servers.*] reference, the codex mcp subcommand, per-server tool approval modes, and the /mcp runtime command.
codex exec
Complete reference for codex exec — scripted invocation, stdin piping, JSON event streams, output formats, exit codes, timeouts, and automation patterns for CI, git hooks, and shell pipelines.
Codex Configuration
Complete config.toml reference for Codex CLI — model selection, approval policies, sandbox modes, profiles, MCP server stubs, shell environment, notify hooks, and project trust levels.
Codex CLI Overview
Install and use OpenAI's Codex CLI — the open-source agentic coding tool. Covers authentication, interactive mode, headless exec, ~/.codex/ layout, and AGENTS.md project memory.
Code Review
A practical guide to reviewing and authoring pull requests — small PRs, naming, control flow, error paths, security, performance, and GitHub PR conventions.
Claude Tool Use (Function Calling)
Define tools, handle tool calls, run agentic loops, use parallel tools, and manage errors with the Claude API.
Claude Code Subagents
Spawn isolated subagents with the Task tool — Plan, Explore, general-purpose, project-defined agents, isolation modes including worktrees, background runs, and orchestration patterns.
Claude Code Statusline
Customise the Claude Code statusline — settings.json keys, the JSON context passed to scripts, available variables (model, session id, cwd, branch, cost), and example scripts in bash, python, and Node.
Claude Code Slash Commands
Complete reference for every built-in Claude Code slash command — session control, context management, configuration, tools, MCP, and authoring custom commands with arguments.
Claude Code Skills
Author and load custom Claude Code skills — how skills are discovered, the SKILL.md schema, available-skills list, packaging, project-vs-user scope, plugin namespacing, and the difference from slash commands.
Claude Code Settings and Permissions
Complete settings.json schema for Claude Code — permission rules, tool allowlists/denylists, environment variables, hooks, MCP, statusline, model selection, and file precedence.
Claude Code Power-User Tips
Advanced Claude Code workflows — effective CLAUDE.md authoring, custom skills, multi-agent patterns, headless scripting, cost control, keyboard shortcuts, prompt caching, and daily workflow techniques.
Claude Code Overview
Install, configure, and use Claude Code — Anthropic's agentic CLI. Covers interactive mode, headless scripting, CLAUDE.md memory files, the project/user settings hierarchy, IDE integration, and authentication.
Claude Code MCP Servers
Add, configure, and build Model Context Protocol (MCP) servers for Claude Code — HTTP, SSE, and stdio transports, management commands, permission rules, and a curated list of useful servers.
Claude Code Hooks
Automate Claude Code lifecycle events with shell hooks — PreToolUse, PostToolUse, UserPromptSubmit, Notification, Stop, SubagentStop, and PreCompact. Covers configuration, environment variables, JSON I/O, exit codes, and blocking examples.
Claude Code CLI
All claude CLI flags, startup modes, non-interactive usage, environment variables, keyboard shortcuts, subcommands, exit codes, and configuration file locations in one place.
Claude API
Complete TypeScript SDK reference for the Anthropic Claude API — install, messages.create, streaming, tool use, vision, types, and Node/Deno/Bun integration.
Claude API
Streaming responses from the Anthropic API — server-sent events, event types, async iteration in Python and TypeScript, partial tool input, error handling, and retry strategies.
Claude API
Complete Python SDK reference for the Anthropic Claude API — messages, streaming, vision, extended thinking, prompt caching, batch processing, and token counting.
Claude API
Anthropic prompt caching — `cache_control`, 5-minute TTL, 1-hour beta, cache breakpoints, cost math, multi-turn caching patterns, and recipes for system prompts, tools, and documents.
Claude API
The Anthropic Files API — upload PDFs, images, and text once and reference them by `file_id` across multiple messages, with citations, lifecycle management, and Workbench integration.
Claude API
The Anthropic Message Batches API — create, poll, retrieve, and stream results at 50% off list price for asynchronous bulk processing of thousands of Claude requests.
Chalk
Apply ANSI colours, backgrounds, and text styles to terminal output in Node.js using Chalk's chainable API, plus comparisons with picocolors and patterns for building polished CLI UX.
Chain-of-Thought Prompting
CoT prompting techniques — zero-shot CoT, few-shot CoT, self-consistency, tree of thoughts, and how reasoning models compare with prompted reasoning.
Bun
Bun is a fast all-in-one JavaScript runtime, package manager, bundler, and test runner written in Zig — a drop-in replacement for Node.js and npm with built-in TypeScript and JSX support.
Branded Types
Branded (a.k.a. nominal, opaque, tagged) types add a phantom marker to a primitive so the compiler refuses to mix two strings — useful for IDs, units, validated input, and money. Covers hand-rolled brands, type-fest's Opaque/Tagged, Zod's .brand(), class-based brands, and runtime validation pairings.
Biome
Rust-based all-in-one linter and formatter for JS/TS/JSON/CSS/GraphQL. Single binary, single config, 10-100x faster than ESLint+Prettier.
Big-O
A practical Big-O reference — common data structures, algorithms, amortized analysis, space vs time, and language-specific gotchas for Python, JavaScript, and TypeScript.
BeautifulSoup
Parse, search, and mutate HTML/XML with BeautifulSoup 4. Covers parser choice (html.parser/lxml/html5lib), find/find_all/select, tree navigation, attribute access, and pairing with requests/httpx/playwright for end-to-end scraping.
Bash
Comprehensive Bash scripting reference covering variables, parameter expansion, control flow, functions, arrays, string manipulation, arithmetic, traps, process substitution, and the Bash 5.3 in-shell command substitution forms.
Astro
Astro is a multi-page, content-first web framework with an islands architecture — server-render Markdown, MDX, and component pages to static HTML, then hydrate interactive widgets selectively with React, Vue, Svelte, or Solid.
argparse
Parse command-line arguments with Python's stdlib argparse module. Covers positional/optional args, subparsers, nargs, validation, mutually exclusive groups, FileType, env-var fallbacks, and argcomplete.
Approvals & Sandboxing
Control what Codex CLI can do — approval policies (untrusted, on-request, never), sandbox modes (read-only, workspace-write, danger-full-access), OS-native sandbox mechanics, and --full-auto.
.d.ts Files
Authoring .d.ts files — ambient declarations, declare module 'foo', asset typing (*.svg?raw), declare global, triple-slash refs, and the home-hero.svg?raw pattern used in this project.
wrangler
Cloudflare's official CLI for building, configuring, and deploying Workers, Pages, KV, R2, D1, Vectorize, Hyperdrive, Queues, Workflows, and Secrets.
diff2html-cli
Convert unified diffs and git diff output into styled HTML side-by-side or line-by-line diff views from the command line.