@drzl/generator-mcp

Generate a Model Context Protocol server from a Drizzle schema: one tool module per table, five tools per table, and the table's CHECK constraints reaching the model as bounds on the arguments it is allowed to write.

The reason this exists

An MCP tool hands a model a schema and the model writes arguments against it. Every other way of building one of these from a Drizzle schema derives that schema from the column types, so the model learns that age is an integer and nothing else. It guesses a value, the write reaches the database, and the database refuses it.

DRZL parses the table's CHECK constraints, so the same tool advertises:

{ "type": "integer", "minimum": 18, "maximum": 120 }

and the model never writes the invalid row. A CHECK that compares two columns cannot be a keyword in any schema language, so those are named in the tool's description instead, which is the only place a model can learn they exist.

Install

npm install -D @drzl/generator-mcp
npm install @modelcontextprotocol/server

Add it to drzl.config.ts:

export default {
  schema: './src/db/schema.ts',
  generators: [
    { kind: 'zod', path: './src/validators/zod' },
    {
      kind: 'mcp',
      path: './src/mcp',
      validation: { useShared: true, importPath: 'src/validators/zod' },
    },
  ],
};

useShared is what carries the constraints. Without it the tool schemas are emitted inline from the column types alone, which still runs and still validates, but the bounds that make this generator worth having come from the validation generator's output.

What it emits

Per table, into path:

| Tool | Arguments | Annotations | | ---------------- | ------------------------ | --------------------------------------- | | users_list | limit, offset | readOnlyHint, idempotentHint | | users_get | the primary key | readOnlyHint, idempotentHint | | users_create | the insert schema | destructiveHint: false | | users_update | { where, data } | idempotentHint | | users_delete | the primary key | destructiveHint, idempotentHint |

A table with no primary key keeps list and create and loses the three that address a row. A materialized view keeps list and get, because the database refuses every write to one.

Plus index.ts, which exports createServer() and registerAllTools(server), and stdio.ts, a runnable entry point an MCP client's command can point at:

{
  "mcpServers": {
    "shop": { "command": "node", "args": ["./dist/mcp/stdio.js"] }
  }
}

The handlers are stubs. list and get return empty; create, update and delete throw Not implemented. Filling them in is the part only you can write, and the row type each one is annotated with is a compile error until the shape is right.

Which SDK

Two generations exist and they are different packages with different rules. Measured on 2026-08-11 by running both:

| | @modelcontextprotocol/sdk (v1) | @modelcontextprotocol/server (v2) | | --- | --- | --- | | zod | works | works | | arktype | throws at registration | works | | valibot | throws at registration | works, through toStandardJsonSchema |

v1 types inputSchema as a zod schema or raw shape, so anything else fails with inputSchema must be a Zod schema or raw shape, received an unrecognized object when the server starts. v2 takes any Standard Schema that also carries ~standard.jsonSchema.

sdk: 'v2' is the default for that reason. sdk: 'v1' is available for a project already on it, and the generator refuses v1 with a non-zod library rather than emitting a server that dies on startup.

Under valibot the emitted tools wrap each schema in toStandardJsonSchema from @valibot/to-json-schema, because valibot's ~standard carries no jsonSchema property. Without the wrapper the tool registers cleanly and advertises no arguments at all, which is a failure nothing reports.

Options

| Option | Default | What it does | | --------------- | --------- | -------------------------------------------------------- | | path | outDir | Where the modules are written | | sdk | 'v2' | Which SDK generation the emitted code imports | | serverName | 'drzl' | The name reported at initialize | | serverVersion | '0.1.0' | The version reported at initialize | | stdio | true | Also emit the runnable stdio entry point | | naming.toolPrefix | none | Placed in front of every tool name: db.users_list | | naming.routerSuffix | none | Appended to each module name and registrar | | naming.procedureCase | none | Casing for file names, identifiers and tool-name stems |

Licence

Apache-2.0. Generated output is yours under your own project's licence.