AI Development & Programming: Build Apps with AI

Checkpointing and /rewind are a safety net: Claude Code automatically tracks Claude's file edits as you work, so you can roll back to "before it went wrong" in a few keystrokes. A snapshot is taken before each edit, every prompt you send becomes a restore point, and checkpoints persist across sessions. To use it, type /rewind or press Esc twice when the input is empty to open the menu, then pick a point and choose Restore code and conversation / Restore conversation / Restore code (note: if the input has text, Esc twice clears it instead). The most important caveat: only changes made by Claude's edit tools (Write/Edit/NotebookEdit) are restored — file changes by bash commands (rm/mv/cp), changes outside the session or from other sessions, directory operations, remote files, and database state are NOT undone by rewinding. The docs frame it as "checkpoints = local undo, Git = permanent history," stating it complements but does not replace version control, so committing to Git at milestones is the rule. /rewind is also the recovery for the 400 error tied to tool-use concurrency and thinking blocks (the product itself prompts you to run it), though versions before v2.1.156 may not clear it so claude update comes first. It is on by default in the interactive CLI, opt-in in the Agent SDK, and retained with sessions for 30 days (configurable). Based on the official documentation, with uncertainties flagged.

Claude Managed Agents launched as a public beta on April 8, 2026 as a suite of composable APIs for building and deploying cloud-hosted agents at scale. Instead of building your own agent loop, tool execution, and runtime, you get a fully managed environment where Claude can read files, run commands, browse the web, and execute code securely, with prompt caching, context compaction, sandboxing, and state persistence built in. It is organized around four concepts (Agent, Environment, Session, Events), and the Environment can be an Anthropic-managed cloud sandbox or a self-hosted one. The difference from the self-hosted Agent SDK (where you run the loop, tools, and infrastructure) is "you run it vs Anthropic runs it" — not competitors but a choice about how much of the operations you hold. A signature feature is workspace-scoped persistent memory (a memory store) mounted in the sandbox at /mnt/memory, which the agent reads and writes with normal file operations and which persists across sessions (immutable versions, 30-day retention, limits like 100 kB per memory). Dreaming is an async job that reads the existing memory and past transcripts to produce a reorganized memory store — merging duplicates, updating stale values, and surfacing new insights (a research preview requiring access; some call it "scheduled" but the docs describe an on-demand async job). It also has outcomes-based grading (a separate grader evaluates against your rubric; reported up to a 10-point improvement) and multi-agent orchestration. Pricing is tokens + $0.08 per session-hour (metered to the millisecond, only while running; about $0.705 for a 1-hour Opus 4.8 session). Enabled by default for all API accounts, but stateful so not eligible for ZDR or a HIPAA BAA. Based on official information, with uncertainties flagged.

Claude Code plugins bundle skills, subagents, hooks, MCP configuration, and other extensions for distribution. A marketplace is a catalog listing where to fetch them. This article explains the official and community catalogs, registration, installation and enabled state, then walks through building a skill, validating its plugin and catalog, and distributing them through Git using one consistent directory layout. It also covers installation scopes, version-dependent update conditions, and what a safety review does not guarantee.

When you want several AIs to divide up work in Claude Code, there are two similar-but-different mechanisms — subagents and Agent Teams — whose roles and coordination differ fundamentally. This article sorts them out accurately. Subagents are a built-in feature: the main agent automatically delegates a specific task to a helper that has its own context window, system prompt, and tool permissions, then receives only a summary (hierarchical, started per task, the helper does not see your conversation history; defined in .claude/agents/ YAML files that you ask Claude to write or edit directly, with built-ins like Explore and Plan, and nesting by default up to 3 layers below the main conversation). Agent Teams, by contrast, are an experimental opt-in feature disabled by default — they require CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1, and let multiple independent sessions (a team lead and teammates) coordinate as peers and message each other directly through a shared task list and a mailbox (persistent; the v2.1.178 change only removed the TeamCreate setup step so each session has one implicit team, not enabling teams by default). The article covers the decisive differences (hierarchical vs peer, summary vs direct messaging, built-in vs experimental flag, and that nesting is a subagents feature while Teams are flat), which to use (subagents when you want only the result or to avoid polluting context, Agent Teams for parallel work where workers must share and self-coordinate, and a single session for sequential work, the same files, or quick fixes), a usage cheat sheet, and Agent Teams caveats (high token cost, 3-5 teammates recommended, no worktree isolation so files conflict, /resume limits, and split panes needing tmux/iTerm2) — all based on the official documentation.

Claude Design is an Anthropic Labs design tool where you describe what you want in conversation and Claude generates UI designs, prototypes, slides, and one-pagers, which you refine via chat, inline comments, direct edits, and sliders (launched April 17, 2026 as a research preview, with over a million users in the first week). The June 17, 2026 major overhaul sharply shrank the designer-developer round-trip. This article covers what Claude Design is (it ran on Opus 4.7 at the April launch, but the June announcement does not restate the model so we do not assert it), the June overhaul (design-system imports from a GitHub repo / design files / raw uploads so Claude builds with your real components and checks its output, two-way sync with Claude Code via /design-sync, direct canvas editing with drag/resize/align and many stability fixes, a token-burning fix via shared usage limits with chat/Cowork/Claude Code, enterprise brand controls where an admin approves and locks a standard system, and expanded export connectors to Adobe/Canva/Miro/Vercel/Wix and PDF/PowerPoint), the two directions of /design-sync (Code: pull the design system into the repo and build with real components; Design: push your code back to the canvas to keep editing; and a Design-to-Code handoff that continues from existing work instead of a screenshot, plus /design from the terminal), availability (a Pro/Max/Team/Enterprise beta at no extra charge, off by default on Enterprise, the canvas web/desktop only and /design-sync in the CLI), and why it matters (closing the rebuild-from-a-screenshot gap and connecting designers and developers in one line) — all based on official information, with uncertainties flagged.

On June 18, 2026, Anthropic shipped Claude Code Artifacts (beta), a feature that turns a terminal coding session into a live web page your team can share. Instead of streaming endless git diff and logs as text, Claude Code can publish an annotated PR walkthrough, a self-updating dashboard, an incident timeline, a release checklist that checks itself off, or an architecture map as one page at a private claude.ai URL. This article explains what Artifacts is (built from the whole session and MCP-connector data, and the open page refreshes in place as work progresses), how it differs from 2024 claude.ai canvas Artifacts (session-sourced, self-updating, org-only and not publishable), what it is good for, how to use it (no /artifact command — you ask in plain language, Claude writes a .html and asks permission to publish, prints the URL, Ctrl+] reopens, each update is a new version at the same URL, Share grants org access, view-only), its limits (a capture of work not an app — no backend, a strict CSP blocks external requests, single page, only .html/.htm/.md, 16 MiB cap, more tokens), and availability (Team/Enterprise beta, must be signed in via /login so API keys cannot publish, Anthropic API only and not Bedrock/Vertex/Foundry, disabled under CMEK/HIPAA/ZDR, plus admin controls and an audit log) — all based on the official documentation.

When Claude Code throws "Not logged in · Please run /login", "Invalid API key", "This organization has been disabled", or "OAuth token has expired", these are mostly 401/403 authentication (who-are-you) problems. This article covers the number-one true cause (an environment variable ANTHROPIC_API_KEY silently overriding your subscription Pro/Max login by precedence, which produces unexpected pay-as-you-go charges, organization disabled, and Invalid API key; the key often comes from .zshrc/.bashrc/.profile, direnv/dotenv, an IDE terminal .env, a leftover from a previous job, or CI), how to detect it (/status to see the active credential, env | grep ANTHROPIC) and fix it (unset ANTHROPIC_API_KEY plus removing it from your shell config), other causes (token revoked/expired, system clock skew, a locked macOS Keychain, a missing Console role causing 403, OAuth redirect failures over WSL/SSH/containers fixed by pasting the code, and server-side org policy that cannot be overridden locally), where credentials are stored (macOS Keychain, Linux ~/.claude/.credentials.json, Windows %USERPROFILE%), the diagnostic workflow (/status → env grep → unset → /logout → /login → clock/Keychain/Console role), and how to tell it apart from usage limit (quota), 429 (rate), 529/500 (server), and Credit balance (prepaid balance) — all based on official information.

You installed Claude Code, but typing claude gives "zsh: command not found: claude", "bash: claude: command not found", or "is not recognized as an internal or external command" on Windows. In most cases the install dir is simply not on your PATH, and the install itself succeeded. This article explains how the shell searches PATH folders, the install methods and locations (the native installer is recommended and lands in ~/.local/bin, Windows %USERPROFILE%\.local\bin; npm needs Node 18+ and installs the same native binary; Homebrew/WinGet; installing only the VS Code extension does not add claude to PATH), the main causes and fixes (add ~/.local/bin to PATH and restart the terminal, an npm EACCES permission error should switch to native rather than sudo, Node too old, multiple-install conflicts checked with which -a / where.exe and reduced to one native install, and the native-binary-not-found case from skipping optional deps), Windows-specific traps (the wrong-shell mix-up like running irm in CMD, restarting the terminal, the old Claude Desktop WindowsApps Claude.exe conflict, and CLAUDE_CODE_GIT_BASH_PATH for Git Bash), auto-update and updating (claude update, claude install, claude doctor for the update result, DISABLE_AUTOUPDATER / DISABLE_UPDATES), and the diagnostic workflow (claude doctor to which -a to PATH to removing extras to a native reinstall) — all based on official information.

On a corporate machine or over VPN, Claude Code fails to connect with "Unable to connect to API", "Unable to connect to API (ECONNREFUSED)", "SSL certificate verification failed", or "fetch failed" — these are network errors where the request never reached Anthropic server (api.anthropic.com), which is different from auth (401/403), server overload (529/500), and rate limiting (429). This article covers the three enterprise blockers (an unconfigured proxy, a TLS inspection proxy replacing certificates, and a firewall blocking domains) plus DNS/VPN/Docker, proxy setup (HTTPS_PROXY/HTTP_PROXY/NO_PROXY, authenticating proxies, SOCKS unsupported, NTLM/Kerberos via an LLM gateway with ANTHROPIC_BASE_URL, and MCP servers needing the vars in their own env), TLS and corporate CA certs (recent Claude Code trusts both its bundled CA set and the OS trust store so a corporate root in the OS store often works with no config; otherwise point NODE_EXTRA_CA_CERTS at the PEM, mTLS via CLAUDE_CODE_CLIENT_CERT/KEY, and curl --cacert at install time), the critical security rule to never use NODE_TLS_REJECT_UNAUTHORIZED=0 (it exposes all traffic including api.anthropic.com to man-in-the-middle attacks), the firewall allowlist domains (api.anthropic.com, claude.ai, platform.claude.com, downloads.claude.ai, raw.githubusercontent.com, with statsig/sentry optional), the diagnostic workflow (curl -I https://api.anthropic.com for reachability, /doctor and proxy check, cert/proxy settings, a direct connection to confirm, then DNS/VPN/Docker), and how to tell it apart from auth/server/rate by whether the request reached the server — all based on official information.

When Claude Code suddenly stops with "API Error: 529 {\"type\":\"overloaded_error\",\"message\":\"Overloaded\"}" or "500 Internal server error", these are transient server-side events — not a mistake in your request or settings, and not your usage running out. This article explains the meaning of 529 Overloaded (Anthropic API temporarily over capacity, congestion across all users) and 500 (an unexpected internal error, with related 504 timeout_error; 502/503 usually come from upstream infrastructure), the fact that neither consumes your usage quota, how Claude Code auto-retries up to 10 times with exponential backoff before showing anything (Retrying in Ns, attempt x/y; CLAUDE_CODE_MAX_RETRIES default 10, API_TIMEOUT_MS default 10 minutes), the user fixes (wait and retry, switch model with /model since capacity is per model so Sonnet often works when Opus is busy, check status.claude.com, /feedback with request_id if a 500 persists), how to tell it apart from confusable errors (529/500 = server-side and no quota used, 429 = your rate limit with a retry-after header and quota, usage limit = plan allowance, 400 = a bad request), developer guidance (typed SDK exceptions and auto-retry, exponential backoff plus jitter, retry-after only on 429, --fallback-model, Priority Tier/Batch), and how to tell a transient spike from a continuing incident — all based on official information.

Working in Claude Code, you suddenly see "Claude usage limit reached. Your limit will reset at 3pm" and stop cold. This is not an error or a bug: it is how the Pro/Max subscription usage limits work. This article explains the two-tier structure (a rolling 5-hour window that recovers ~5 hours after your first prompt, plus a weekly window that resets every 7 days, and on Max a separate weekly cap just for Opus), the fact that Claude Code and the Claude apps share the same plan allowance, the four biggest consumption drivers (model choice where Opus burns far more than Sonnet, context size, long continuous sessions, and subagents/MCP), five ways to keep working when you hit the cap (drop to Sonnet with /model, trim context with /compact, wait out a 5-hour window, switch to pay-as-you-go API, or buy credits / upgrade), how to see what is left (/usage, /status, and Settings to Usage for the weekly reset date), and the difference between subscription limits and API limits (429, retry-after, tiers). Because the exact numbers get revised over time, it avoids asserting current figures and recommends checking the live official view.

Claude Code reports "Prompt is too long" when total input, including history, files, and tool results, exceeds the context limit. This article separates compacting a long history, reducing an oversized first input, and resolving an underlying compaction error such as authentication failure. MCP definitions load on demand by default, while 1M availability depends on the model, connection, and plan. It also explains token counting and stop reasons for direct API use.