TubeMCP defines 2 tools with clear verb-based names (youtube_search, youtube_get_transcript) and reasonable descriptions (190+ chars each). Both tools have input schemas with typed parameters and descriptions. However, there are significant gaps: (1) output schemas are not explicitly documented in the code, return types are inferred from runtime behavior (list[dict] | str, dict | str) rather than declared; (2) error handling returns unstructured strings instead of actionable error guidance; (3) no pagination support despite search returning potentially large result sets; (4) missing parameter constraints (e.g., max_results_per_query lacks min/max bounds); (5) tool descriptions lack dependency hints and are somewhat generic; (6) no tool annotations (readOnlyHint, idempotentHint). The server avoids multi-concern tools and uses natural identifiers (video_url accepts URL or ID), which is good.

• Document output schemas explicitly. For youtube_search, declare that it returns List[{video_id, title, channel_name, duration_seconds, publish_date, thumbnail_url}]. For youtube_get_transcript, declare {video_id, title, channel_name, duration_seconds, publish_date, thumbnail_url, transcript: List[{text, start, duration}]}.
• Replace unstructured error strings with a structured ErrorResponse containing code, message, and recovery_suggestion. Example: {'code': 'INVALID_VIDEO_ID', 'message': 'Invalid YouTube URL or video ID', 'recovery_suggestion': 'Ensure the URL is a valid YouTube link (youtu.be/...) or a valid video ID.'}
• Add parameter constraints: max_results_per_query should have minimum=1, maximum=20 (or a reasonable cap). Declare this in both the parameter description and type definition.
• Add pagination to youtube_search: include a limit parameter (default 10, max 50) and return a next_cursor or has_more flag. This prevents context window overflow and guides the agent to paginate if needed.
• Enhance tool descriptions with dependency hints: 'Call youtube_search first to find relevant videos. Once you identify a promising video, use youtube_get_transcript to fetch its full transcript.' This guides multi-step workflows.
• Add tool annotations: set readOnlyHint=true and idempotentHint=true for both tools so LLMs know they are safe to retry.
• Consider validating input ranges at tool invocation time and returning a clear error message (e.g., 'max_results_per_query must be between 1 and 20') rather than silently clamping or allowing arbitrary values.