a0ce1f89be
The spec never uses the phrase "structured output". It defines two separate things under Tool Result: "Structured Content" (the `structuredContent` field) and "Output Schema" (the `outputSchema` field). Collapsing them into "structured output" conflates the two. It is also actively confusing here. In LLM tooling "structured output" means constrained decoding — making the *model* emit conforming JSON. These clients call a model API, so a reader could reasonably take the phrase to mean the tool constrains the model's response, which is the opposite of what is going on: the tool describes the shape of its own result. Headings and prose now say "structured content". References to real identifiers are left alone: the Python SDK's own docs page is called Structured Output and lives at docs/servers/structured-output.md, and its decorator parameter is `structured_output`. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
27 lines
1.3 KiB
Markdown
27 lines
1.3 KiB
Markdown
# A Simple MCP Weather Server written in Go
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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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## Building
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```bash
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go build -o weather
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```
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## Running
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```bash
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./weather
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```
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The server will communicate via stdio and expose two MCP tools:
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- `get_forecast` - Get weather forecast for a location (requires latitude and longitude)
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- `get_alerts` - Get weather alerts for a US state (requires two-letter state code)
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## Structured content
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Both tools advertise an `outputSchema` and return `StructuredContent`. `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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`get_forecast` sets no `OutputSchema` on the `Tool`: the SDK infers one from the handler's return type, which is the idiomatic Go spelling. `get_alerts` overrides it, because inference widens a slice to `["null", "array"]` — a nil slice marshals to `null` — and the tool never returns nil.
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Note that an array-rooted schema requires a `2026-07-28` client: the SDK sends it as written on every connection rather than projecting it down, so an older client rejects the tool list.
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