mcp-extensions

Overview ¶

Example: typed MCP tools — one tool per verb.

Each tool is a thin wrapper around a method on the blog store. The args struct says exactly what the tool needs (no "optional unless action=…" gymnastics), the return type is a concrete domain object that gets JSON-marshaled and advertised via `outputSchema` on tools/list, and every handler reads like normal Go — no map[string]any assertions.

One tool is kept on the older builder API (search_posts) so the two shapes stay visible side by side. Use the typed shape for new tools and the builder when you need to hand-tune a schema the typed generator doesn't emit yet.

Try it:

go run ./examples/mcp-extensions &

# tools/list now carries inputSchema AND outputSchema for typed tools.
curl -s -X POST localhost:8080/mcp -H 'Content-Type: application/json' \
     -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | jq .

curl -s -X POST localhost:8080/mcp -H 'Content-Type: application/json' \
     -d '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{
            "name":"create_post",
            "arguments":{"title":"hello","author":"ada","content":"first","tags":["intro"]}
          }}'

# Validation: required field missing surfaces through the MCP error envelope.
curl -s -X POST localhost:8080/mcp -H 'Content-Type: application/json' \
     -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{
            "name":"create_post","arguments":{"title":"hello"}
          }}'