Open Source Tool Compiler

Forge once.
Run everywhere.

Define your tools once. Compile to MCP servers, TypeScript SDKs, OpenAPI specs, docs, eval harnesses, and agent‑optimized schemas.

Get Started See the Schema

tools.anvil.yaml → 10 targets

anvil: "1.0"
service:
  name: weather-tools
  version: "1.0.0"

tools:
  get_current_weather:
    description: Get current weather for a location
    agent:
      when_to_use:
        - User asks about current weather
      tips:
        - Prefer city names over coordinates
    parameters:
      location:
        type: string
        required: true
      units:
        type: enum
        values: [celsius, fahrenheit]
    permissions:
      - type: network
        target: api.weather.com
    side_effects: none
    cost: low

The tool layer is fragmented.

Every agent runtime has its own schema format. Every integration needs its own docs, permissions, and tests. You maintain seven versions of the same definition that drift apart.

MCP schema

OpenAPI spec

TypeScript types

Agent descriptions

Permission declarations

Test suites

Human docs

Anvil replaces all of them with a single source of truth.

One schema. Full semantics.

Anvil captures everything agents need — not just types. Descriptions optimized for LLMs, cost indicators, side effects, permissions, and examples that become test cases.

agent.description

Rich context for LLM tool selection — separate from human docs

when_to_use

Explicit scenarios where this tool is the right choice

when_not_to_use

Anti-patterns — redirect agents to better alternatives

permissions

Declared per-tool, enforced at runtime. Network, filesystem, env, db

side_effects

none / read / write / destructive — agents know the blast radius

cost

free / low / medium / high / variable — agents can budget

examples

Input/output pairs that become eval test cases automatically

errors + agent_hint

Known failure modes with recovery instructions for agents

Ten targets. Zero config.

anvil compile --target mcp — no config file needed. All targets are built into the CLI. Or use --all for everything.

⚡

MCP Server

Fully typed Model Context Protocol server with tool handlers and annotations.

@anvil-tools/target-mcp

📐

OpenAPI 3.1

Complete spec with schemas, security, examples, and error responses.

@anvil-tools/target-openapi

📘

Documentation

Markdown docs with parameter tables, examples, and agent guidance.

@anvil-tools/target-docs

🧠

Agent Schema

LLM-optimized tool schema with agent descriptions and few-shot examples.

@anvil-tools/target-agent-schema

🧪

Eval Harness

Test suite with schema validation, contract testing, and agent eval.

@anvil-tools/target-eval

📦

TypeScript SDK

Typed client class with Zod runtime validation.

@anvil-tools/target-sdk-ts

⌨️

CLI Application

Commander-based CLI with subcommands and JSON output.

@anvil-tools/target-cli-gen

🔌

Claude · GPT · Vercel AI

Native tool formats for Anthropic, OpenAI, and Vercel AI SDK.

target-anthropic / target-openai / target-vercel-ai

Try it live.

Edit the YAML on the left. See generated outputs update instantly on the right.

tools.anvil.yaml1 tool detected
anvil: "1.0"
service:
  name: weather-tools
  version: "1.0.0"

tools:
  get_weather:
    description: Get current weather
    agent:
      description: |
        Use this tool for real-time weather data.
        Best for current conditions.
      when_to_use:
        - User asks about current weather
      tips:
        - Prefer city names over coordinates
    parameters:
      location:
        type: string
        required: true
        description: City name
      units:
        type: enum
        values: [celsius, fahrenheit]
        default: celsius
    returns:
      type: object
      properties:
        temperature:
          type: number
        conditions:
          type: string
    permissions:
      - type: network
        target: api.weather.com
    side_effects: none
    cost: low
    idempotent: true
    examples:
      - name: basic
        input:
          location: San Francisco
          units: celsius
        output:
          temperature: 18
          conditions: Partly cloudy
        prompt: "What's the weather in SF?"

import { Server } from '@modelcontextprotocol/sdk/server/index.js';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';

const server = new Server(
  { name: 'weather-tools', version: '1.0.0' },
  { capabilities: { tools: {} } },
);

server.setRequestHandler(ListToolsRequestSchema, async () => ({
  tools: [
    {
      name: 'get_weather',
      description: "Use this tool for real-time weather data.\n        Best for current conditions.",
      inputSchema: {
        type: 'object',
        properties: {
          "location": { "type": "string", "description": "City name" },
          "units": { "type": "enum" }
        },
        required: ["location"],
      },
    }
  ],
}));

const transport = new StdioServerTransport();
await server.connect(transport);

Compiler architecture.

Like protobuf compiles .proto to language-specific code, Anvil compiles .anvil.yaml through an IR. Adding a target is one interface.

Source

.anvil.yaml
or TypeScript

Parse + Validate

Generate

Target Plugins

Output

MCP · API · SDK
Docs · Eval · CLI

Featured tools.

Real-world tool definitions ready to compile. Install with anvil install <name> or browse all tools.

github-tools

Issues, PRs, search, comments, and repo browsing

5 tools·githubdevtools

anvil install github-tools

postgres-tools

Read-only queries, table schemas, and guarded mutations

3 tools·databasesql

anvil install postgres-tools

weather-tools

Current conditions and multi-day forecasts

2 tools·weatherapi

anvil install weather-tools

browser-tools

Navigate, screenshot, and extract links from any URL

3 tools·browserautomation

anvil install browser-tools

Get started in 30 seconds.

npm install -g @anvil-tools/cli

anvil init my-tools && cd my-tools

anvil compile --target mcpZero config — MCP server generated

anvil serve --stubLive MCP server for Claude Desktop / Cursor