The server exposes 20 tools with STDIO transport, wrapping the crawl4ai library. Tool definitions are present in crawl4ai_mcp/core/tool_guides.py with names, descriptions, and input schemas. However, quality varies significantly. Strong points: most tools have descriptive names (verb-prefixed), detailed parameter descriptions for complex tools like crawl_url and batch_crawl, and documented input schemas with type constraints. Weak points: 9 tools (deep_crawl_site, crawl_url_with_fallback, extract_structured_data, extract_youtube_transcript, get_youtube_video_info, batch_extract_youtube_transcripts, search_google, search_and_crawl, batch_search_google) have only placeholder descriptions ('Crawl multiple related pages from a website', 'Crawl URL with fallback strategies...') and NO visible input schemas in the provided source. Output schemas are documented for a few tools (e.g., crawl_url mentions metadata-only response, file path return), but most lack explicit return type documentation. Error handling exists (timeout, overwrite rejection, max URL limits) but lacks actionable recovery guidance. No tool annotations (readOnlyHint, destructiveHint, idempotentHint) despite many tools being read-only or idempotent. Security: no credentials in parameters (good), but no permission gates or scope declarations.

• Complete schemas for all 9 underdefined tools (deep_crawl_site, extract_youtube_transcript, search_google, etc.) with at least input parameters, types, and per-parameter descriptions. Use tools like crawl_url and batch_crawl as templates.
• Add explicit output schemas to every tool documenting return type, field names, and structure. Example for batch_crawl: { type: 'array', items: { type: 'object', properties: { success: boolean, url: string, output_file?: string, error?: string } } }.
• Annotate all tools with readOnlyHint=true (crawl_url, search_google) and idempotentHint=true (get_supported_file_formats, get_youtube_api_setup_guide). No tools appear destructive, so destructiveHint is not needed.
• Expand placeholder descriptions to 50-150 chars. Example: 'deep_crawl_site: Extract content from multiple related pages on a domain. Follows internal links up to specified depth. Returns array of pages with text, metadata, and optional media. Use when a single page won't suffice and you need site-wide context.' Instead of 'Crawl multiple related pages from a website'.
• For tools returning arrays (search_google, batch_extract_youtube_transcripts), add limit and offset/page parameters to enable pagination. Default limit=20, max=100.
• Document error recovery paths in descriptions. Example for batch_crawl: 'If a URL times out, the tool will retry with extended timeout. If still failing, that result will appear in the response with success=false and error reason. Retry by calling crawl_url on that URL individually with a longer timeout.'