MCP server valv

@valv/mcp

Point it at a database URL. Your agent queries it safely. No SQL, no code.

A zero-config MCP server built on valv. Give it a connection string and it introspects your live schema, serves four tools (list_resources, search_resources, describe_resource, query) read-only by default, and enforces your policies — no SQL ever reaches the model, and it can only read what you allow.

Works with PostgreSQL, MySQL, SQLite, CockroachDB, ClickHouse, and MongoDB.

Guided setup

The fastest way in — it probes your database, lets you choose access, and writes the config:

npx @valv/mcp init

It takes either a connection string or individual fields (host, port, user, password, database), confirms the dialect, connects and shows your tables, then offers read-only / pick-tables / a policy-file stub. It then merges the server entry into the client of your choice — Claude Code, Claude Desktop, Cursor, or Codex — at project or global scope, leaving any existing config in place. Lastly it offers to install the valv skill, which teaches the agent how to query valv and turn results into interactive chart-report HTML files — as a skill for Claude Code (.claude/skills), Codex (.agents/skills), or Cursor (.cursor/skills), at project or global scope. Finally it can copy a kickstart prompt to your clipboard — paste it into your agent to explore the schema (seeding .valv/notes.md for future queries) and generate a single interactive valv-map.html overview of the database.

Manual setup

Add it to your .mcp.json (or Claude Desktop config):

{
  "mcpServers": {
    "db": {
      "command": "npx",
      "args": ["-y", "@valv/mcp"],
      "env": { "DATABASE_URL": "postgresql://user:pass@localhost:5432/mydb" }
    }
  }
}

For ClickHouse, use its HTTP URL and a database name:

"env": { "DATABASE_URL": "http://localhost:8123", "VALV_DATABASE": "analytics" }

For MongoDB, use a standard connection string. Set VALV_DATABASE when the URL does not select a database:

"env": { "DATABASE_URL": "mongodb://localhost:27017", "VALV_DATABASE": "analytics" }

Configuration

All via environment variables:

Variable	Description
DATABASE_URL	Connection string (required; or pass as the first CLI arg).
VALV_PROVIDER	postgresql | mysql | sqlite | mongodb | clickhouse. Inferred from the URL when omitted.
VALV_DATABASE	Database name for ClickHouse or MongoDB.
VALV_TABLES	Comma-separated allow-list — only these tables are exposed.
VALV_EXCLUDE	Comma-separated deny-list, applied after the allow-list.
VALV_POLICY_FILE	Path to a policy module (below) for tenant scoping / hidden fields.
VALV_CONTEXT	JSON context the policy reads (e.g. {"tenant":{"id":"acme"}}).
VALV_HTTP_PORT	Serve over Streamable HTTP on this port instead of stdio.

Policy file

Without one, access is read-only across all tables. To restrict what the agent can see — which tables, which columns — point VALV_POLICY_FILE at a module that receives the configured valv instance:

// valv.policy.cjs
module.exports = (valv) => {
  valv.policy("orders", () => ({
    read:   true,                          // allow reads (or { column: value } to filter rows)
    fields: { deny: ["internal_notes"] },  // hide columns from the agent
  }))
  // Tables without a policy are denied (deny-all).
}

Need per-request row scoping by tenant/user? That belongs in the app-controlled path, where your code supplies real identity per request — use @valv/mcp-sdk (or pass a fixed VALV_CONTEXT and read it in the policy here).

License

MIT