youtube-summarize

Instructions

Implementation Reference

• main.py:123-162 (handler)

  The summarize_transcript tool handler decorated with @mcp.tool(). It fetches a YouTube video transcript, extracts metadata (language, type, video ID), and returns formatted output with instructions, metadata, and the transcript text for the LLM to summarize.

  @mcp.tool()
  def summarize_transcript(
      url: str,
      prompt: str | None = None,
      languages: list[str] | None = None,
  ) -> str:
      """Fetch a YouTube video's transcript and return it with summarization instructions.
  
      The LLM client should use the returned instructions and transcript to produce a summary.
  
      Args:
          url: YouTube video URL or video ID
          prompt: Custom summarization instructions. If omitted, a default summary prompt is used.
          languages: Preferred languages in priority order (e.g. ["en", "de"]). Defaults to English.
      """
      try:
          video_id = extract_video_id(url)
      except ValueError as e:
          return f"Error: {e}"
  
      langs = languages or ["en"]
      try:
          transcript = api.fetch(video_id, languages=langs)
          text = TextFormatter().format_transcript(transcript)
  
          instructions = prompt or DEFAULT_SUMMARY_PROMPT
          language = transcript.language
          language_code = transcript.language_code
          is_generated = transcript.is_generated
  
          return (
              f"[INSTRUCTIONS]\n{instructions}\n\n"
              f"[METADATA]\n"
              f"Video ID: {video_id}\n"
              f"Language: {language} ({language_code})\n"
              f"Type: {'auto-generated' if is_generated else 'manual'}\n\n"
              f"[TRANSCRIPT]\n{text}"
          )
      except Exception as e:
          return _handle_transcript_error(e, video_id, langs)

• main.py:123-123 (registration)

  Registration of the summarize_transcript tool using the @mcp.tool() decorator from FastMCP framework.

  @mcp.tool()

• main.py:25-28 (helper)

  DEFAULT_SUMMARY_PROMPT constant - default summarization instructions used when no custom prompt is provided to the summarize_transcript tool.

  DEFAULT_SUMMARY_PROMPT = (
      "Summarize the following YouTube video transcript. "
      "Provide a concise overview of the main topics, key points, and conclusions."
  )

• main.py:37-47 (helper)

  extract_video_id helper function - parses YouTube video URLs or bare IDs to extract the 11-character video ID used by summarize_transcript.

  def extract_video_id(url_or_id: str) -> str:
      """Extract a YouTube video ID from a URL or bare ID string."""
      url_or_id = url_or_id.strip()
      if BARE_ID_REGEX.match(url_or_id):
          return url_or_id
      match = VIDEO_ID_REGEX.search(url_or_id)
      if match:
          return match.group(1)
      raise ValueError(
          f"Could not extract a YouTube video ID from: {url_or_id}"
      )

• main.py:58-88 (helper)

  _handle_transcript_error helper function - converts youtube_transcript_api exceptions into user-friendly error messages used by summarize_transcript.

  def _handle_transcript_error(e: Exception, video_id: str, languages: list[str] | None = None) -> str:
      """Convert youtube_transcript_api exceptions into user-friendly error strings."""
      from youtube_transcript_api import (
          AgeRestricted,
          InvalidVideoId,
          IpBlocked,
          NoTranscriptFound,
          RequestBlocked,
          TranscriptsDisabled,
          VideoUnavailable,
      )
  
      if isinstance(e, TranscriptsDisabled):
          return f"Error: Transcripts are disabled for video '{video_id}'."
      if isinstance(e, NoTranscriptFound):
          lang_str = ", ".join(languages) if languages else "any"
          return (
              f"Error: No transcript found for video '{video_id}' "
              f"in language(s): {lang_str}. Use list_transcripts to see available languages."
          )
      if isinstance(e, VideoUnavailable):
          return f"Error: Video '{video_id}' is unavailable."
      if isinstance(e, InvalidVideoId):
          return f"Error: '{video_id}' is not a valid YouTube video ID."
      if isinstance(e, AgeRestricted):
          return f"Error: Video '{video_id}' is age-restricted and cannot be accessed."
      if isinstance(e, IpBlocked):
          return "Error: YouTube is blocking requests from this IP address."
      if isinstance(e, RequestBlocked):
          return "Error: The request to YouTube was blocked."
      return f"Error fetching transcript for '{video_id}': {e}"