mcp-codegen

The official MCP TypeScript SDK requires modeling MCP Tool Schema using a type-system called Zod. mcp-codegen allows you to leverage plain-old-TypeScript-objects.

Installation

``bash
npm install mcp-codegen
`

Build

This package is built using esbuild to transpile TypeScript to ES2015 (ES6) for broad compatibility. The build process generates both JavaScript and TypeScript declaration files.

`bash
npm run build:all
`

Exports

The package exports the following components:

- McpRequired() - Decorator for required fields
- McpOptional() - Decorator for optional fields
- Format(format: string) - Decorator for field format specification
- SchemaBuilder - Function to generate Zod schema from decorated classes
- Primitives - TypeScript type for primitive values
- ZOD_METADATA, ZOD_PROPS - Internal constants

Dependencies

1. TypeScript experimental decorators (legacy only, TC39 coming soon)
1. Reflect and reflect-metadata
1. Zod to JSON Schema (Zod4 coming soon)

Getting Started

$3

Build MCP Tool schema using TypeScript classes and decorators.

`ts
import { McpRequired, McpOptional, Format } from "mcp-codegen";

export class ToolCallInput {
im_just_a_prop: string;

@McpRequired()
query: string;

@McpRequired()
async: boolean;

@McpOptional()
max?: number;

@Format('bigint')
@McpOptional()
variance?: number;

@McpOptional()
queryId?: string;

@Format('date-time')
@McpOptional()
createdAt?: string;
}
`

$3


`ts
import { ToolCallInput } from "decorated-typescript-class";
import { SchemaBuilder } from "mcp-codegen";
import zodToJsonSchema from "zod-to-json-schema";

const zodObject = SchemaBuilder(ToolCallInput);
const jsonSchema = zodToJsonSchema(z.object(zodObject));
`

#### Generated JSON Schema

`json
{
"type": "object",
"properties": {
"query": {
"type": "string"
},
"async": {
"type": "boolean"
},
"max": {
"type": "number"
},
"variance": {
"type": "integer",
"format": "int64"
},
"queryId": {
"type": "string"
},
"createdAt": {
"type": "string",
"format": "date-time"
}
},
"required": [
"query",
"async"
],
"additionalProperties": false,
"$schema": "http://json-schema.org/draft-07/schema#"
}
`

$3

`ts
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";

new McpServer().registerTool(
"example-tool",
{
title: "Example Tool",
inputSchema: toolSchema // Output of SchemaBuilder
},
(args: ToolCallInput): Promise => {
return Promise.resolve({
content: [
{
type: "text",
text: Results for query: ${args.query} // Required type
},
{
type: "text",
text: Results requested: ${args.max || 100} // Optional type
}
]
});
}
)
``