What Claude Code Is
The agentic CLI/IDE tool explained — the session loop, install, and where everything lives.
Claude Code Cheat Sheet
One printable page of Claude Code flags, commands, shortcuts, permission modes and file locations — every line checked against the official docs on 2026-10-13.
The claude CLI: Flags That Change Outcomes
An opinionated tour of the Claude Code command line — the five-flag contract for unattended runs, the recorded-system-prompt trap, and how --bare, --safe-mode and --restricted differ.
CLAUDE.md & Memory Files
The highest-leverage Claude Code customization: persistent project memory.
AGENTS.md & Cross-Tool Interop
The open standard every coding agent reads — and how to keep it in sync with your CLAUDE.md.
Plan Mode
Investigate and propose before any edits run — the safest way to tackle big changes, and the blocks it does not enforce.
IDE Integrations
VS Code and JetBrains extensions, inline diffs, and shared settings.
settings.json: The Config System
File tiers and precedence, key sections, and project vs personal config.
Permissions & Permission Modes
allow/ask/deny rules and modes — cut prompts without losing safety.
Agent SDK Permissions: the Six-Step Order
Every permission bug in a headless agent is an order bug. The six steps the Agent SDK evaluates — which ones can only deny, which can only allow, and the five ways allowedTools silently does nothing.
Sandbox Credential Masking: keep tokens working, keep them secret
Mask environment variables, JWTs, AWS SigV4 pairs, and credential files so sandboxed commands authenticate without ever seeing the real secret. Config, gotchas, and OS matrix.
Custom Slash Commands
Turn a repeatable workflow into one word.
The /design Command: Artboards Before Code
Claude Code's /design skill drafts editable UI artboards before writing a line — how it works, when it wins, and the gotchas nobody documents.
Output Styles
Change Claude Code's tone, verbosity, and teaching behaviour.
Statusline Customization
The statusline is a shell script that gets the whole session as JSON on stdin — model, context window, cost, rate limits, PR state, and prompt-cache health. Which fields actually earn their place, the update triggers that fire it, and three recipes including a cache-health line that surfaces the quietest cost leak in long sessions.
Spec-Driven Development with Spec Kit
Stop vibe-coding big features. Make an executable spec the source of truth, then have Claude Code build from it — with GitHub's Spec Kit.
Context Management
/compact vs /clear, auto-compaction, and staying effective as sessions grow.
Context Budget Audit: /skill-doctor, Output Caps and the Six Numbers That Fill Your Window
A 20-minute audit for a Claude Code project that has grown slow, forgetful, or expensive. Measure with /context and /usage, prune the skill listing with /skill-doctor and skillOverrides, cap tool output with bashOutputMaxChars and taskOutputMaxChars, keep CLAUDE.md out of subagents with omitClaudeMd, and set the auto-compact window on purpose. Every number cited to the September 2026 Claude Code docs.
Checkpoints & Rewind
Undo Claude's edits, roll back a whole session, and compress context with /rewind — the safety net for ambitious runs.
Hooks: Deterministic Automation
Run commands at lifecycle events to enforce formatting, gates, and safety.
Skills: On-Demand Expertise
SKILL.md, progressive disclosure, and Skill vs command vs subagent vs MCP.
Subagents & Parallel Agents
Delegate to isolated-context agents with scoped tools — and when not to.
Subagent Fleet Limits: Concurrency Caps & Nested Depth
On July 21, 2026 Claude Code capped concurrent subagents at 20 and killed nested spawning. Three days later nesting came back at depth 3. Here are the four env vars, the error you'll hit, why the caps exist, and how to design fleets that survive them.
Dynamic Workflows & ultracode
Orchestrate tens to hundreds of subagents from a script Claude writes — for codebase audits, large migrations, and cross-checked research.
Cross-Session Messaging
Make two Claude Code sessions talk to each other — the native SendMessage / ListAgents tools shipped in Claude Code 2.1.224, the @mention syntax, the trust boundary, and when to use messaging vs. subagents vs. worktrees.
Projects: The Coordinator & Parallel Threads
On September 17, 2026 Claude Code Projects became an orchestration layer: a coordinator that scopes and delegates, and threads that are full cloud sessions, each on its own branch and repo copy. Here is the architecture, how it differs from subagents and worktrees, what it costs against your usage limits, and the eligibility rule that explains why you may not have it yet.
MCP Servers in Claude Code
Connect databases, GitHub, browsers and more via the Model Context Protocol.
Background Tasks, /loop & Scheduling
Long-running commands, recurring loops, and scheduled cloud agents.
Auto-Commit Background Agents: Draft-PR Handoff
On July 1, 2026 Claude Code v2.1.198 let background agents commit, push, and open a draft PR on their own. Five weeks later v2.1.221 tuned the default. Here is what the flow actually does, the notification hook it fires, why the community wanted an off switch, and the propose-only pattern that still works.
Plugins & Marketplaces
Bundle skills, agents, commands, hooks and MCP into one installable unit — and install other people's. The three install scopes and their precedence, the three marketplace trust tiers, the always-on context cost every enabled plugin charges you, and the eight commands that cover the whole lifecycle.
Mods: In-Process Extensions
Mods are TypeScript middleware that runs inside Claude Code — rewrite tool calls, prompts, turns, and the interface itself.
Plugin Evals: Test Your Plugin with claude plugin eval
Prove a Claude Code plugin actually helps — write eval cases, grade them with six grader types, read the with/without delta, mock MCP servers, and gate CI on the score.
Git Worktrees & Parallel Workstreams
Run multiple isolated Claude sessions on one repo without them colliding.
Parallel Agents at Merge Time: Intent Conflicts and the CI Wall (2026)
Worktrees stop agents from overwriting each other's files. They don't stop two plans that can't both be true from merging cleanly. The coordination layer above Git (Foremerge's protocol, decoded) plus the CI surgery Linear did when agents started adding 2,000 tests a week — with every number.
Headless Mode & the Agent SDK
Run Claude Code in CI, and build production agents on the same harness.
Cloud Sessions: the VM Claude Code runs in when it isn't your laptop
Practitioner guide to Claude Code cloud sessions and cloud environments — exactly what carries over from your machine and what silently doesn't, the four network access levels and the four paths that bypass them, network secrets, setup scripts vs SessionStart hooks, the ~5-minute cache rule, resource and time limits, and the --cloud/--teleport round trip.
Self-Hosted Environments: run cloud sessions on your own boxes
Practitioner guide to the claude self-hosted-runner beta (shipped Aug 7, 2026 in v2.1.224). Run Claude Code web, mobile and desktop cloud sessions on infrastructure you control — egress-only, no inbound holes, one-user-at-a-time isolation. Architecture, quickstart, runner lifecycle, git creds, autoscaling, and the six gotchas that catch every first fleet.
The MCP Token Tax
Why connecting MCP servers can burn 50k–150k tokens before your first request — and the three fixes: Tool Search, code execution, and knowing when a CLI call wins.
Accessibility
Screen reader mode, vim ergonomics, mouse and scroll controls, and high-contrast themes in Claude Code.
Troubleshooting Claude Code
Symptom-to-fix for hangs, high memory, broken search, compaction thrashing, and garbled terminals.
Feature Flags: Why Your Claude Code Isn't Mine
Claude Code switches features on with flags it fetches from Anthropic. Privacy env vars, Bedrock, gateways and fresh installs silently turn that fetch off — here's exactly what you lose and how to pin behavior instead.