Impit

Impit

Use this skill when work touches Apify Impit: browser-impersonating HTTP requests via TLS + HTTP fingerprints, without running a real browser.

Workflow

1. Inspect the local Impit surface before changing code:
   • Language binding: Node impit (npm), Python impit (PyPI/conda), or Rust crate from git.
   • Package/native binary versions and platform (Node ≥ 20; platform-specific optional deps).
   • Client lifetime: shared Impit / AsyncClient / Impit::<Jar> vs one-shot clients.
   • Fingerprint choice: generic chrome/firefox vs versioned / okhttp / ios18.
   • Session needs: cookies, proxies, HTTP/3, redirects, default headers, timeouts.
2. Refresh docs when the user asks for latest fingerprints, option names, or binding differences. Start from source-map.md.
3. For Node/TypeScript install, ImpitOptions, fetch, responses, and errors, use nodejs.md.
4. For Python and Rust APIs, patched deps, and builder patterns, use python-rust.md.
5. For fingerprints, HTTP/3 vs proxy constraints, cookies, headers precedence, multipart boundaries, and Crawlee ImpitHttpClient, use fingerprints-ops.md.
6. Implement in the existing project style:
   • Prefer bun / bunx in command examples for Node work.
   • Reuse one client instance per impersonated identity (pool + optional cookie jar).
   • Do not treat Impit as a headless browser — no page JS, DOM, or automation APIs.

Judgment

• Impit mimics TLS ClientHello and HTTP fingerprints (headers, HTTP/2 settings, pseudo-headers). Plain fetch / axios / undici fail TLS JA3-style checks; Impit addresses that layer.
• Prefer Impit when bot detection blocks non-browser clients and a full browser is unnecessary. Prefer a real browser (Playwright/Puppeteer) when the site requires executed JavaScript or interactive flows.
• Default clients are stateless for cookies until you pass cookieJar (JS), cookie_jar/cookies (Python), or with_cookie_store (Rust).
• HTTP/3 and proxies are mutually unsupported in current docs — do not enable both.
• Header precedence (case-insensitive): per-request headers > instance headers > browser impersonation defaults. Empty-string values remove an impersonated header.
• Generic chrome / firefox auto-pick a version; use versioned fingerprints when detection tracks outdated signatures.
• One Impit instance = one user-agent identity sharing config, pool, and jar. Create separate instances for distinct identities.
• Response bodies are single-consume (Fetch-compatible). Do not call text()/json()/arrayBuffer() twice.
• Respect site ToS, robots, rate limits, and applicable law. Use impersonation for legitimate integrations, scraping within policy, and testing — not for unauthorized access or abuse.

Verification

Prefer the repo's existing checks. For meaningful Impit work, include the relevant subset:

• Smoke request to a known endpoint; assert status and body parse once.
• Confirm negotiated protocol when http3: true (response.http_version in Python; inspect logs/headers where available).
• Proxy path: HTTP/HTTPS/SOCKS without HTTP/3; fail closed if both are configured.
• Cookie round-trip when a jar is configured (set on first response, sent on second).
• Platform install: native optional dependency resolves on the target OS/arch (glibc vs musl on Linux).
• Typecheck Node consumers against ImpitOptions / RequestInit / error classes.
• Crawlee: crawler runs with ImpitHttpClient and expected fingerprint option.