Conventions MCP Server

conventions-mcp

Personal memory for durable coding conventions and standing instructions — one store, any MCP-compatible AI client, available in every project. It holds rules like "always use 2-space indent in this language," "never force-push to main," lasting corrections, and long-lived workflow preferences that should carry across future sessions rather than get re-explained every time. It is deliberately not a history of individual jobs or a place for task-specific directions, temporary decisions, current status, or one-off commands.

Why this one

There's no shortage of memory MCP servers — several well-established ones (mem0/OpenMemory, Zep/Graphiti, the official reference memory server, plus a long tail of smaller projects) already do "remember things across sessions." What's different here:

• Narrow taxonomy, not a general note-taking store. Every capture must be a durable rule for future work and gets classified into one of five purpose-built types — convention, instruction, correction, preference, other — plus a project field and topic tags. Task-specific procedures and work history are excluded so retrieval stays precise instead of noisy.
• Deterministic retrieval, not best-effort. Most memory MCPs rely entirely on the calling model noticing a tool description is relevant and deciding to call it — which fails silently and inconsistently. Codex and Claude Code hooks force the agent to call list_rules: SessionStart supplies the instruction, while PreToolUse denies every other tool until the call has happened.
• Transparent by default, not silent. Every capture and update echoes the verbatim stored content and whether it's global or project-scoped back immediately, so a misheard or misclassified rule is visible and correctable on the spot — not something you discover three sessions later via search.
• Fully local at runtime. SQLite + local embeddings, no hosted service, no per-token costs, no API key. The embedding model is downloaded once on first use (or explicitly with conventions-mcp warmup) and then runs locally. Classification (type/topics/projectScoped) is done by the calling agent at capture time, guided by the tool description — it already has the full conversation the thought came from, richer context than an isolated content string would give a separate extractor model.
• Project-scoped without fuzzy matching. A rule can be global (the default) or tied to one specific codebase. Stdio clients derive the project from their working directory; HTTP clients provide an MCP root or an X-Conventions-Project header. The project identifier is never guessed by an LLM from free text.

If what you want is a general-purpose "remember everything" store, or you're not on Claude Code and don't need the hook-driven determinism, one of the more general options above may fit better. This one is for someone who specifically wants a tight, coding-convention-focused memory that stays accurate and doesn't require trusting the model to remember to check it.

What it's tuned to store

Every capture is classified into one of five types by the calling agent, guided by capture_thought's tool description (src/server.js):

Each thought also gets 1–3 topic tags for filtering. This is deliberately narrow — it's not a general note-taking store — but the taxonomy isn't hardcoded logic, it's just the wording of the tool description and its zod schema in src/server.js. Retuning what counts as a convention vs. an instruction, or adding a new type, is a matter of editing that description text, not restructuring the code. The one wrinkle: the five type names are also referenced in the type filter's enum in list_thoughts (src/server.js) — if you rename or add a type, update that enum too or the new type will get rejected as a filter value. Everything's stored as a JSON blob column, so none of this needs a schema migration.

Separately, every thought gets a project field — null by default (applies everywhere), or a specific project id if it's scoped to the current codebase. The calling agent only judges whether it's project-scoped (projectScoped); the actual project id is derived deterministically from the working directory — the absolute path with separators turned into dashes, e.g. /var/www/html → -var-www-html, matching the per-project directory name Claude Code itself uses under ~/.claude/projects/. The model never names the project, so retrieval can do an exact match instead of fuzzy text comparison.

• Storage: SQLite (better-sqlite3) + sqlite-vec for native vector search, FTS5 for keyword search, combined via reciprocal rank fusion. One file, no server, no daemon.
• Embeddings: local, via Xenova/bge-small-en-v1.5 (384-dim, quantized, ~130MB). Downloads once, loads lazily, and needs no GPU.
• Classification: done by the calling agent (Claude Code, or any MCP client) at capture time, guided by the tool description — no network call, no external model, no API key.
• Transport: MCP over stdio by default, with an optional localhost-only Streamable HTTP mode for running it as a persistent service.
• Proactive retrieval: Codex and Claude Code hooks (see below) load or enforce standing rules at every context boundary — no project instruction file to keep in sync, no dependence on the model happening to notice a tool description is relevant.
• Scoped retrieval: list_rules and semantic search return global rules plus the current project's rules; project-specific rules from other codebases stay out of normal retrieval. list_thoughts remains the explicit all-records management view.

Setup

Two ways to get this: a git checkout (if you want to read/modify the source) or the npm package (if you just want it running).

Git checkout:

npm install
npm run init-db        # creates data/memory.db

npm package:

npm install -g conventions-mcp
conventions-mcp init-db    # creates ~/.conventions-mcp/memory.db
conventions-mcp warmup     # downloads and verifies the embedding model

Nothing to configure — there's no API key and no external service. MEMORY_DB_PATH is the only environment variable this reads, and it's optional (see .env.example).

Persistent local service

Use Streamable HTTP when the MCP client should connect to one boot-managed server instead of launching a stdio child for every session:

MCP_TRANSPORT=http MCP_HTTP_HOST=127.0.0.1 MCP_HTTP_PORT=47123 conventions-mcp

Run that command under the operating system's service manager and configure the MCP client with http://127.0.0.1:47123/mcp. See docs/shared-service.md for complete systemd, launchd, and Windows setup and verification instructions. The server rejects non-local host headers when bound to localhost. MCP_HTTP_HOST defaults to 127.0.0.1 and MCP_HTTP_PORT defaults to 47123.

HTTP clients that support MCP roots need no additional project configuration. For clients that do not, set X-Conventions-Project to the absolute project path in project-local MCP configuration. An HTTP session without either value receives global rules only and cannot create a project-scoped capture, which prevents one project's rules from leaking into another project.

Register with Claude Code

Register at user scope so it's available in every project, not just one repo — use the claude mcp add CLI, not a hand-edited config file:

# Git checkout — an absolute path, since Claude Code may spawn this from an
# arbitrary working directory:
claude mcp add --scope user conventions -- node /absolute/path/to/conventions-mcp/src/server.js

# npm package — already on PATH:
claude mcp add --scope user conventions -- conventions-mcp

Either way, this writes to ~/.claude.json's mcpServers key, which is what the CLI actually reads; a mcpServers entry placed directly in ~/.claude/settings.json is silently inert. Verify with claude mcp list. A new Claude Code session is required to pick up a newly-registered server.

Codex standing-rule hook

hooks/hooks.json contains user-scoped Codex SessionStart and PreToolUse hooks. The first tells the agent to call list_rules; the second denies every other tool until that call happens. The gate is re-armed after /clear and compaction, when the loaded rules leave context. The rules themselves are not placed in hook output, so a large rule set cannot be truncated before the agent receives it from the MCP tool.

Install it as ~/.codex/hooks.json. If that file already contains hooks, merge this file's SessionStart and PreToolUse entries instead of replacing the existing configuration. The hook expects the MCP server to be registered as conventions, matching the setup command above, and the installed conventions-mcp command to be on PATH. Open /hooks once in Codex to review and trust the newly installed hooks; a new session is required before a startup hook can fire.

Claude Code standing-rule hooks

Three hooks in ~/.claude/settings.json enforce list_rules before tool use — the first two provide reminders, the third actually enforces it:

{
  "hooks": {
    "SessionStart": [
      { "hooks": [{ "type": "command", "command": "node /absolute/path/to/conventions-mcp/bin/session-rules.js", "timeout": 15 }] }
    ],
    "UserPromptSubmit": [
      { "hooks": [{ "type": "command", "command": "node /absolute/path/to/conventions-mcp/bin/prompt-reminder.js", "timeout": 5 }] }
    ],
    "PreToolUse": [
      { "matcher": "*", "hooks": [{ "type": "command", "command": "node /absolute/path/to/conventions-mcp/bin/pre-tool-check.js", "timeout": 5 }] }
    ]
  }
}

• bin/session-rules.js fires at session start and emits a short reminder to call list_rules first — rather than embedding rule content in the hook output directly, which doesn't scale (a large enough stored rule set gets silently truncated to a small preview before it ever reaches the model). It also re-arms the enforcement gate after a compaction or /clear (the two events that drop the already-loaded rules from context), so a reload is forced then too.
• bin/prompt-reminder.js fires on every turn with a static reminder to follow the loaded conventions and to capture only genuinely durable rules intended for future sessions or repeated work. It explicitly excludes task-specific directions, temporary choices, current status, incident history, one-job commands, and records of how an individual job was completed.
• bin/pre-tool-check.js fires before every tool call and denies it outright until list_rules has run this session — the first two hooks are advisory (reminders only), so this is the layer that actually enforces the requirement. It's forced once per session, not once per turn.

None of the three touch the database directly. list_rules resolves the current project from the stdio working directory, an MCP root, or the HTTP project's X-Conventions-Project header.

npm package: the scripts live inside the global install rather than a known clone path — resolve it first with npm root -g, then point the hook at $(npm root -g)/conventions-mcp/bin/session-rules.js the same way.

Windows: point the command at the .cmd wrapper instead of the .js file directly (no node prefix — the batch file invokes it) — bin\session-rules.cmd / bin\prompt-reminder.cmd / bin\pre-tool-check.cmd for a git checkout, or the equivalent path under npm root -g for the npm package.

Tools

Notes

• If a single message states several distinct rules, capture_thought gets called once per rule, each relayed individually — not merged into one capture or summarized together.
• The database lives at data/memory.db in a git checkout, or ~/.conventions-mcp/memory.db for the npm package (override either with MEMORY_DB_PATH). It's gitignored and created with private permissions. Use conventions-mcp backup <absolute-destination> for a live-safe, integrity-checked backup. docs/shared-service.md shows a scheduled setup.
• To upgrade embedding quality later without re-architecting, swap MODEL_NAME in src/embeddings.js — but re-embed existing thoughts if the new model's vector space isn't compatible with the old one (different models' embeddings aren't comparable, even at the same dimension).