McpForge

Value

Problem. Shipping a custom MCP server means wrestling SDK wiring, stdio rules, and sandbox mistakes before Cursor/Claude Desktop ever see a tool.

How it helps. TypeScript MCP server starter over stdio with echo, fetch_url (guards), and notes_fs sandbox tools — fork, rename, extend.

Why buy. Save an afternoon of MCP SDK + Cursor JSON + path guards; own a minimal server that hosts already expect.

• Official @modelcontextprotocol/sdk + stdio transport
• Sample tools: echo, fetch_url, notes_fs
• Private-host / size guards on fetch; path sandbox for notes

How it works

flowchart LR
  Host["Cursor / Claude Desktop"] -->|stdio JSON-RPC| Server["McpForge"]
  Server --> Echo["echo"]
  Server --> Fetch["fetch_url"]
  Server --> Notes["notes_fs ./notes"]

Mermaid flowchart (render in GitHub / VS Code / mermaid.live).

Use case

From Cursor, call notes_fs write ideas.md then echo to confirm the MCP server is live.

What you get

• McpServer wiring in src/server.ts
• Three sample tools + Vitest (20 tests)
• Cursor / Claude Desktop config snippets in README
• MIT license

Project structure

mcpforge/
  src/
    index.ts, server.ts
    tools/   echo, fetchUrl, notesFs
    lib/     sandbox, fetchGuards, textResult
  tests/ notes/

Quick start

npm install && npm test && npm run build
Point Cursor mcp.json command to dist/index.js (absolute path)
Restart Cursor — tools: echo, fetch_url, notes_fs

Example

From src/tools/echo.ts

// Register with server.registerTool(...)
// echo: { message, uppercase? } → text result
// Keep handlers pure; inject deps for Vitest.

Design decisions

• Log only to stderr — stdout is the MCP protocol channel
• Pure tool handlers with injected fetch/notesRoot for offline tests
• Block localhost/private IPs in fetch_url by default

Limitations

• Not a hosted MCP cloud
• stdio only in the starter (no HTTP transport sample)
• fetch_url is GET-oriented with guards — not a general browser
• You must use absolute paths in host MCP config

Who it’s for

Developers connecting custom tools to Cursor or Claude Desktop.

Not for: Anyone wanting a managed multi-tenant MCP hosting product.

What you own

Full MIT-licensed TypeScript source via Gumroad ZIP. Fork it, ship it commercially, keep the license notice. You are responsible for secrets, hardening, and production ops.

Related

AgentForge · PromptKit · RagPipe · EvalHarness

Demo