docs

name	docs
description	Use when answering questions about or writing code against a named third-party library/framework. Fetches fresh, authoritative documentation via Context7 (`ctx7`) instead of relying on stale training data. Fires both reactively ("how do I X with library Y") and proactively (about to write library code and unsure of current API). Skip for language stdlib and general CS concepts.
allowed-tools	Bash, WebFetch

Docs (Context7 Library Lookup)

Fetch fresh, authoritative third-party library documentation via the ctx7 CLI instead of guessing from (possibly stale) training memory.

When to use

USE when:

• The user asks "how do I X with library Y" for a named third-party library or framework.
• You are about to write code against a named third-party library and are not 100% sure the API still matches your training memory.
• A question is version-specific ("in the latest FastAPI…", "post-v18 React…").

SKIP when:

• The question is about a language stdlib (Python stdlib, JS built-ins, Go stdlib, etc.) — you already know these and ctx7 is wasted tokens.
• It's a general CS/programming concept, not a library.
• The code in question lives in the current repo — read the source directly instead.
• You've already fetched the same library+topic earlier in this session — reuse that answer.

Two-step workflow

Context7 splits lookup into a name→ID resolution step and a docs-fetch step.

Step 1: Resolve library name to a Context7 ID

npx ctx7 library <name> "<query>"

Always pass a query — per ctx7 library --help it's positional-optional, but Context7 uses it to rank candidate libraries by relevance and results get noticeably worse without it. The command returns several candidates; pick the first result unless it's obviously wrong for your query (e.g., a fork, translated mirror, or unrelated namespace match).

Example:

npx ctx7 library react "useEffect cleanup function"
# → /reactjs/react.dev  (first result)
# → /websites/react_dev  (second result)
# → /facebook/react      (fifth result — canonical repo, but not always top-ranked)

Step 2: Fetch docs for the resolved ID

npx ctx7 docs <libraryId> "<query>"

Unlike ctx7 library, both arguments are required on ctx7 docs — omitting the query produces error: missing required argument 'query' and exits 1.

Example:

npx ctx7 docs /reactjs/react.dev "useEffect cleanup function"

Returns curated doc snippets ranked for the query, with source URLs.

When to skip Step 1

Only skip the library step when you already resolved the ID earlier in the current session and you're reusing it. Do not guess IDs from intuition — the highest-ranked match is often not what you'd expect (/reactjs/react.dev, not /facebook/react; /pola-rs/polars, not /polars/polars).

Efficiency rules

• Don't re-query the same library+topic twice in one session. Reuse the first result from earlier in the conversation.
• Prefer specific queries over broad ones. "useEffect cleanup" beats "hooks"; "scan_parquet glob pattern" beats "polars io".
• --json is available on both commands if you need structured output, but plain text is fine for reading into your own context.

ctx7 vs WebFetch

• Reach for ctx7 first whenever the target is a named library — it returns curated, query-ranked snippets rather than raw HTML.
• Fall back to WebFetch for arbitrary URLs (blog posts, GitHub issues, RFCs, changelogs not yet indexed by Context7).

Auth / setup

• The first npx ctx7 invocation auto-installs the package; no manual setup needed.
• Works anonymously. If you hit rate limits or auth errors, run npx ctx7 login and retry.

Common mistakes

• Guessing the library ID instead of running ctx7 library first. IDs are not predictable (/reactjs/react.dev, /pola-rs/polars). Resolve first unless you already saw the ID earlier in this session.
• Using ctx7 for stdlib questions. Wasted tokens — you already know list.sort().
• Re-running the same query multiple times in one session instead of reusing the first output.
• Ignoring errors. ctx7 exits 1 and prints ✖ … or error: … on bad IDs, missing queries, or unknown names. If the output looks like an error, it IS — don't proceed as if you got docs. Re-run ctx7 library with a different name or fall back to WebFetch.