fetch-crawl4ai

name	fetch-crawl4ai
description	Deep URL fetch using crawl4ai (Playwright-powered) for JS-rendered pages, anti-bot sites, and dynamic content. Slower than fetch-jina but handles sites that block simple fetchers. Requires user-installed crawl4ai package.
version	0.1.0
layer	leaf
domains	["web-fetch"]
scenarios	["url-reading","js-heavy","anti-bot-site","dynamic-content"]
trigger_keywords	["fetch","深抓","crawl","JS 渲染","playwright","动态页","anti-bot"]
model_tier	Standard
auth_required	false
cost	free
experience_digest	experience.md

Deep URL fetch through crawl4ai, backed by Playwright and Chromium. Use this as the fallback when fetch-jina fails, refuses a URL, returns an empty page, or cannot see JavaScript-rendered content.

Input Fit

• JavaScript-heavy SPAs where server HTML is mostly empty.
• Anti-bot or dynamic sites that block simple HTTP fetchers.
• Pages that need a CSS selector wait before extraction.
• Public pages where a local Chromium browser can render the content.

Invocation

Call fetch.py's sync fetch(url: str, wait_for: str | None = None, timeout_seconds: float = 30.0) function:

result = fetch("https://example.com/app", wait_for=".loaded")

Successful calls return:

{
    "ok": True,
    "markdown": "...",
    "title": "Rendered page title",
    "url": "https://example.com/final-url",
    "meta": {
        "status_code": 200,
        "backend": "crawl4ai",
        "browser": "chromium",
        "elapsed_sec": 2.4,
    },
    "source": "https://example.com/app",
}

Failure Modes

• Missing crawl4ai package returns reason: crawl4ai_unavailable. Install with pip install crawl4ai plus playwright install chromium, or fall back to fetch-jina.
• Browser or crawl4ai runtime failures return reason: crawl4ai_runtime_error with the error message or stderr tail.
• DNS, connection, and transport failures return reason: network_error.
• Slow pages that exceed timeout_seconds return reason: timeout.
• HTTP 403 or detectable challenge pages return reason: anti_bot_blocked; degrade to fetch-playwright or fetch-firecrawl paid fallback.
• Successful crawls with empty or too-short Markdown return reason: empty_content.

Limits

• Requires user opt-in installation: pip install crawl4ai.
• Requires a Chromium browser installed for Playwright: playwright install chromium.
• This tool is slower and heavier than fetch-jina; use it only when a simple fetch cannot retrieve the useful content.
• It does not solve sites that require authentication, strong bot mitigation, paid proxies, or long interactive flows.

Quality Bar

• Evidence items have non-empty title and url.
• No crash on empty or malformed API response.
• Source channel field matches the channel name.