brandvoice-mcp

An MCP server that learns your writing style and makes every AI client sound like you.

Quick start

Install

pip install brandvoice-mcp

Configure Claude Desktop

Add to your claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/claude_desktop_config.json):

{
  "mcpServers": {
    "brandvoice": {
      "command": "python",
      "args": ["-m", "brandvoice_mcp"],
      "env": {
        "ANTHROPIC_API_KEY": "sk-ant-...",
        "OPENAI_API_KEY": "sk-..."
      }
    }
  }
}

Set ANTHROPIC_API_KEY and OPENAI_API_KEY in the env block (both required for normal use: Claude for analysis/alignment, OpenAI for chunk embeddings). The server will exit with a clear error if either is missing.

Teach it your voice

In Claude Desktop, ask the model to use ingest_samples with real writing:

Use the ingest_samples tool to learn my writing style from this blog post: [paste content]

The server chunks the text, stores embeddings in ChromaDB, and (for samples of about 50+ words) runs LLM style analysis. Shorter snippets are still stored for retrieval but skip style analysis to avoid unreliable profiles.

Write in your voice

Before any writing task, call get_voice_context with your task and platform. The returned prompt_injection is wrapped in <voice_context>...</voice_context> — prepend it to your request or system prompt.

Use get_voice_context for a LinkedIn post about React performance, then write it in my voice.

Check alignment

After drafting text, call check_alignment with the draft. You get a 0–100 score, drift flags, and rewrite hints against your stored profile and samples.

Use check_alignment on this draft: [paste text]

Tools reference

Tool	Description
ingest_samples	Ingest writing; chunk, embed, and update style profile when thresholds are met
get_voice_context	Voice guidelines, similar samples, and prompt_injection for a task
set_guidelines	Merge explicit brand voice rules (pillars, tone, vocabulary, etc.)
check_alignment	Score how well content matches your voice
get_profile	Full profile: learned style (including profile_source), guidelines, counts
list_samples	Paginated list of ingested samples (each row includes the Chroma document id for delete_samples)
delete_samples	Delete samples by sample_ids (from list_samples) or set all to true to clear the collection; refreshes or resets the learned profile

How it works

Ingestion: Text is split into chunks, embedded with OpenAI (default text-embedding-3-small), and stored in a local ChromaDB collection (writing_samples) for similarity search. The aggregate learned style and explicit guidelines live in ~/.brandvoice/profile.json (human-readable, separate from vectors) so a vector DB issue does not silently wipe your profile alongside embeddings.

Style analysis: For sufficiently long samples, Claude analyzes tone and patterns (including humor, technical depth, and warmth scores used in get_voice_context). If the API fails, a heuristic fallback runs; profile_source records "llm" vs "heuristic". After enough stored chunks (see BRANDVOICE_PROFILE_THRESHOLD), each qualifying ingest re-merges the corpus via Claude (prompts/corpus_aggregate.md) into a single aggregate profile; on failure, the latest per-sample LLM snapshot is used when available.

Writing assistance: For a task, the server retrieves your profile and the top similar chunks, then builds prompt_injection from markdown templates under brandvoice_mcp/prompts/.

Configuration

Variable	Default	Description
ANTHROPIC_API_KEY	(required)	Anthropic API key (style analysis, alignment)
OPENAI_API_KEY	(required)	OpenAI API key (chunk embeddings; Anthropic has no embeddings API)
BRANDVOICE_DATA_DIR	~/.brandvoice	Data directory (profile.json, Chroma persistence)
BRANDVOICE_EMBEDDING_MODEL	text-embedding-3-small	OpenAI embedding model name
BRANDVOICE_ANALYSIS_MODEL	claude-sonnet-4-6	Model for style analysis
BRANDVOICE_PROFILE_THRESHOLD	5	Minimum stored samples before aggregate profile can update after an LLM-analyzed ingest

Model deprecation: If the default claude-sonnet-4-6 is deprecated or unavailable in your region, set BRANDVOICE_ANALYSIS_MODEL to a supported model ID (e.g. claude-opus-4-6 or claude-haiku-4-5-20251001). Claude 4 model IDs use no date suffix; check Anthropic's model documentation for the current list.

Limitations

• Single client: Designed for one MCP client at a time. Multiple clients sharing the same ~/.brandvoice directory may hit SQLite/Chroma lock errors.
• API costs: Style analysis and alignment use Anthropic; chunk embeddings use OpenAI. Each ingest_samples and check_alignment consumes tokens; budget accordingly.

Requirements

• Python 3.11+
• Anthropic API key (ANTHROPIC_API_KEY) — LLM calls
• OpenAI API key (OPENAI_API_KEY) — embeddings for ChromaDB similarity search

Development

git clone https://github.com/jsliapark/brandvoice-mcp.git
cd brandvoice-mcp
pip install -e ".[dev]"
pytest

Architecture (overview)

MCP client (Claude Desktop, Cursor, …)
        │ stdio
        ▼
  brandvoice-mcp server
        │
        ├── profile.json     ← aggregate learned style + explicit guidelines
        └── ChromaDB         ← writing_samples (embeddings + chunks)

Manual testing in a terminal

The server speaks JSON-RPC on stdin/stdout. When you run python -m brandvoice_mcp, it should block until the client disconnects or you press Ctrl+C — there is no interactive prompt.

• Do not type in that terminal while the server is running; random text is not valid JSON-RPC and you will see errors like Invalid JSON / JSONRPCMessage validation errors.
• Do not run two copies of the server on the same stdio session.
• If you use Cursor / Claude Desktop with this project, let only the IDE spawn the process — don’t also run python -m brandvoice_mcp in a terminal unless you are debugging with a real MCP client attached.

If python -m brandvoice_mcp crashes with Server has no attribute tool, your checkout is on the old low-level Server API — use FastMCP (from mcp.server import FastMCP) and sync __main__.py to call run_server() without asyncio.run (see current server.py on main).

For a local run, export both ANTHROPIC_API_KEY and OPENAI_API_KEY (see Configuration above).

License

MIT — see LICENSE.