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`#[tool_handler]` generated `ttl_ms: None, cache_scope: None`, but both are required on a paginated result at 2026-07-28, so a strict client rejected tools/list before it could reach a tool call. The server worked around that by hand-writing list_tools purely to set the two fields. rust-sdk#1120 fixed the macro, released in rmcp 3.1.1: it now emits the fields when the negotiated revision expects them and omits them otherwise. Both lockfiles move to 3.1.2 and the override goes away, so the server is back to the plain `#[tool_handler]` path the SDK documents. Verified on the raw wire: after a 2026-07-28 handshake, tools/list carries `ttlMs: 0` and `cacheScope: "public"` with no code setting them, and the smoke test's strict client still validates both tools' structured content.
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712 B
Markdown
9 lines
712 B
Markdown
# A Simple MCP Weather Server written in Rust
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See the [Build an MCP server](https://modelcontextprotocol.io/docs/develop/build-server) tutorial for more information.
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## Structured content
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Both tools declare an `output_schema` and return `structured_content`. `get_forecast` returns an object; `get_alerts` returns a top-level JSON array, which protocol revision `2026-07-28` is the first to allow — see [Structured Content](https://modelcontextprotocol.io/specification/draft/server/tools#structured-content) in the spec.
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Note that an array-rooted schema requires a `2026-07-28` client: rmcp sends it as written on every connection rather than projecting it down, so an older client rejects the tool list.
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