unclecode / unclecode/crawl4ai
[Bug]: MCP scrape tools lack wait_until / SPA support that REST API and CLI provide
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Description
crawl4ai version
0.8.6
Expected Behavior
MCP scrape tools (crawl4ai_md, crawl4ai_html, etc.) should accept the same wait_until, delay_before_return_html, and cache_mode parameters as the REST API (POST /crawl) and CLI (crwl -c). This would allow MCP-based agents to reliably scrape JavaScript-heavy pages by waiting for content to fully load.
Example desired usage:
{
"url": "https://example.com/dynamic-content",
"wait_until": "networkidle",
"delay_before_return_html": 2
}
Environment
| Component | Version |
|---|---|
| Crawl4AI | 0.8.6 |
| OS | Debian GNU/Linux 12 (bookworm) |
| Python | 3.12.13 |
| Image | unclecode/crawl4ai:latest |
Suggested Fix
- Expose
crawler_configparameters on MCP tool schemas — mapwait_until,delay_before_return_html,cache_mode, etc. to the existing REST/CLI options - Document MCP defaults vs REST/CLI behavior
Acceptance Criteria
- MCP scrape tools accept
wait_untilparameter (load,domcontentloaded,networkidle,commit) - MCP scrape tools accept
delay_before_return_htmlparameter - Documentation clarifies default wait behavior for each interface (MCP vs REST vs CLI)
Current Behavior
MCP tools return immediately after initial DOM load, without waiting for dynamic content. No parameters are exposed to control wait behavior.
- REST API with
crawler_config.wait_until: "networkidle"→ ✅ Complete rendered content - CLI with
-c 'wait_until=networkidle'→ ✅ Complete rendered content - MCP tools → ❌ Incomplete content (dynamic elements missing)
Current workaround: Bypass MCP entirely and use POST /crawl directly.
Is this reproducible?
Yes
Inputs Causing the Bug
Any JavaScript-heavy / AJAX-driven page where content loads after initial page load.
Steps to Reproduce
1. Start Crawl4AI with MCP enabled at `/mcp/sse`
2. Configure any MCP client (e.g., OpenCode) with the Crawl4AI MCP server
3. Call MCP scrape tool:
crawl4ai_md(url="https://example.com/dynamic-content")
4. Observe: Content is incomplete (dynamic elements not rendered)
5. Compare with working REST call:
curl -s http://localhost:11235/crawl \
-H 'Content-Type: application/json' \
-d '{
"urls": ["https://example.com/dynamic-content"],
"crawler_config": {
"wait_until": "networkidle",
"cache_mode": "bypass"
}
}'
6. Observe: REST returns complete rendered content
Code snippets
OS
Debian GNU/Linux 12 (bookworm)
Python version
3.12.13
Browser
No response
Browser version
No response
Error logs & Screenshots (if applicable)
No response
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start at the MCP scrape tool schemas and compare their exposed arguments with the existing crawler_config options used by POST /crawl and crwl -c. Verify the MCP tools on a JavaScript-heavy page, then confirm they accept wait_until and delay_before_return_html and that the documentation explains default wait behavior across MCP, REST, and CLI.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- api, documentation
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 52/100