Skill of the day: claude-api (Claude API & SDK reference)

claude-api is the official Anthropic marketplace plugin that teaches Claude current Claude API and Anthropic SDK patterns so it stops guessing from stale training priors. Register the anthropics/skills marketplace, install claude-api@anthropic-agent-skills, then let it auto-trigger on Claude, Anthropic, or LLM-shaped work. The marketplace description is “Claude API and SDK documentation skill for building LLM-powered applications.” Catalog metadata version: 1.0.0, a marketplace field rather than per-skill semver. Checked 2026-09-21.

What it does

SKILL.md is a reference and workflow guide: detect the project language, read the matching {lang}/ docs, pull concepts from shared/, and write official Anthropic SDK code, or raw HTTP when that is the right surface. The bundled language trees are python/, typescript/, java/, go/, ruby/, csharp/, php/, curl/, plus shared/.

Surfaces the skill names at a high level, rather than as an API encyclopedia:

• Messages-centric Claude API work
• Tool use and Tool Runner
• Managed Agents (beta)
• Caching and compaction, batches, files, and token counting
• Named subcommands: migrate, prompt-audit, upgrade, cost-optimize, managed-agents-onboard

Not the Claude Agent SDK. SKILL.md disambiguates: Tool Runner lives in the regular Anthropic API SDK; Managed Agents is the hosted agent surface; Claude Agent SDK (claude-agent-sdk) is a separate product. This skill covers Claude API and Managed Agents patterns. It does not generate Agent SDK code.

When to use and when not

Use when you are building or editing Claude or Anthropic integrations, migrating models, auditing prompts, upgrading the Anthropic SDK, or running a cost-optimization pass the skill documents.

Do not use when another provider is the job, including OpenAI/GPT, Gemini, Llama, Mistral, Cohere, or Ollama, or when project imports point to those providers. Do not rewrite a non-Anthropic file with Anthropic SDK calls without asking. Do not treat this plugin as a substitute for Claude Agent SDK docs.

Field note: the trigger is broad. Install it when you want Claude or Anthropic work to default into this reference, not as a passive catalog entry you never open.

Install in Claude Code

The anthropics/skills README registers the marketplace:

/plugin marketplace add anthropics/skills

Then either Browse, choose anthropic-agent-skills, choose claude-api, and install, or use the direct marketplace plugin form:

/plugin install claude-api@anthropic-agent-skills

[GAP]: README install bullets still exemplify only document-skills and example-skills. Plugin name claude-api is verified same-day in marketplace.json. Do not invent other install flags.

Walkthroughs on this site: Add Anthropic's skills marketplace, sync Claude.ai skills and plugins into Claude Code, and skill doctor if loading looks wrong.

Limits

• README disclaimer: skills are demo/reference; product behavior may differ from the repo.
• No skill-level README.md: the raw path returned 404 same-day. SKILL.md, {lang}/, and shared/ are the docs.
• Model and pricing tables inside the skill are cached. The skill points at the live Models API and shared/live-sources.md; do not treat radar or skill tables as live rate cards.
• Heavy skill, approximately 86KB for SKILL.md plus many subfiles. Claude loads it on demand; it is not a one-chat toy.
• No invented endpoints, beta headers, model IDs, or pricing are asserted here.

Pair with prior radars

Learn, ship API code, then verify assumptions before pasting rates or model strings from memory.

Sources (checked 2026-09-21)

• marketplace.json, plugin claude-api, skills path ./skills/claude-api, marketplace metadata version 1.0.0
• SKILL.md, name, description, skip rules, language trees, subcommands, and Agent SDK disambiguation
• anthropics/skills README, marketplace add, Browse/install pattern, demo/reference disclaimer, and [GAP] examples omitting claude-api by name
• claude-api skill tree