`mcp-gemini-transcribe-go` MCP Server

This server provides synchronous speech-to-text transcription using Google’s Gemini 3.5 Transcribe model (gemini-3.5-transcribe-preview) via the Vertex genai client.

It is the single-purpose, standalone sibling of the gemini_transcribe tool that is also bundled into the all-in-one mcp-gemini-go server. Both share the exact same implementation via mcp-common, so their behavior can never drift — use this standalone server when you only need transcription and want a minimal surface.

This server uses the synchronous transcription API (the generate_content path on gemini-3.5-transcribe-preview), not the live/streaming API. It is intended for pre-recorded files up to ~15 minutes, not for real-time streaming.

Note: Gemini 3.5 Transcribe is served only in the global location. This server defaults LOCATION to global; leave LOCATION/GOOGLE_CLOUD_LOCATION unset (or set to global) for transcription to work.

Tools

gemini_transcribe

Transcribes a pre-recorded audio file to text using Google’s Gemini 3.5 Transcribe model (synchronous mode). Supports language hints, custom vocabulary biasing, speaker diarization, word-level timestamps, and smart formatting.

Parameters:

• input_audio (string, required): The audio to transcribe — either a local file path or a gs:// URI. Supported formats include WAV, MP3, OGG/Opus, FLAC, M4A/AAC, AIFF, AMR, WEBM, and PCM.
• mime_type (string, optional): The MIME type of the audio (e.g. audio/wav, audio/mpeg, audio/ogg). Inferred from the file extension when omitted (.m4a/.mp4/.aac infer audio/mp4).
• model (string, optional): The transcription model. Defaults to gemini-3.5-transcribe-preview.
• language_codes (string array, optional): BCP-47 language hints (e.g. ["en-US", "es-ES"]). Omit for automatic language detection.
• custom_vocabulary (string array, optional): Up to 1000 phrases (brand names, proper nouns, domain terms) that bias recognition. Most reliable when language_codes is also set.
• enable_diarization (boolean, optional): Label individual speakers (up to 8). Incompatible with smart_formatting.
• enable_word_timestamps (boolean, optional): Return word-level start/end offsets. Incompatible with smart_formatting.
• smart_formatting (boolean, optional): Use SMART mode — filler-word removal, light grammatical cleanup, and automatic formatting. Incompatible with enable_diarization and enable_word_timestamps.
• output_directory (string, optional): Local directory to save the transcription result (JSON) to.
• gcs_bucket_uri (string, optional): GCS URI prefix to store the transcription result (JSON).
• output_filename (string, optional): Base name for the saved transcript. The extension is forced to .json. See Naming Outputs.

The plain transcript is always returned as the first text content item. When speaker diarization or word-level timestamps are requested, a second text content item carries the full structured result as JSON (transcript, per-segment speaker labels, and word timings).

Environment Variable Configuration

The tool utilizes the following environment variables:

• GOOGLE_CLOUD_PROJECT (string): Required. Your Google Cloud Project ID. Note: PROJECT_ID is also supported as a fallback.
• GOOGLE_CLOUD_LOCATION (string): The preferred Google Cloud location. For Gemini 3.5 Transcribe this defaults to global (the only location where the model is served).
  • Fallback: LOCATION is also supported as a fallback for GOOGLE_CLOUD_LOCATION.
• GENMEDIA_BUCKET (string): An optional default Google Cloud Storage bucket to use for GCS outputs if the gcs_bucket_uri parameter is not specified in the tool request.
• PORT (string, for HTTP transport): The port for the HTTP server to listen on. Default: 8080.

Transports Supported

• stdio (default)
• sse (Server-Sent Events)
• http (Streamable HTTP)

CORS is enabled for the HTTP transport, allowing all origins by default.

Run

Build the tool using go build or go install.

• STDIO (Default):

  ./mcp-gemini-transcribe-go
  # or
  ./mcp-gemini-transcribe-go -transport stdio

• HTTP:

  ./mcp-gemini-transcribe-go -transport http
  # Optionally set PORT, e.g. PORT=8084 ./mcp-gemini-transcribe-go -transport http

  The MCP server will be available at http://localhost:<PORT>/mcp.
• SSE (Server-Sent Events):

  ./mcp-gemini-transcribe-go -transport sse

  The MCP server will be available at http://localhost:8081.

Example Usage

Transcribe a GCS audio file

export GOOGLE_CLOUD_PROJECT=$(gcloud config get-value project)

mcptools call gemini_transcribe \
  --params '{"input_audio": "gs://your-gcs-bucket/audio/meeting.wav", "language_codes": ["en-US"], "output_directory": "./transcripts"}' \
  mcp-gemini-transcribe-go

Transcribe with diarization and word timestamps

mcptools call gemini_transcribe \
  --params '{"input_audio": "./samples/interview.mp3", "enable_diarization": true, "enable_word_timestamps": true, "output_directory": "./transcripts"}' \
  mcp-gemini-transcribe-go