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84ffd2d7d2
Both tools declare an OutputSchema and return StructuredContent alongside the text. get_alerts returns []Alert, so it answers with a top-level JSON array rather than an array nested in an object, which protocol revision 2026-07-28 is the first to allow. "No alerts" is simply []. get_forecast returns an object, for contrast. The declared schema narrows the inferred ["null","array"] root to "array": jsonschema-go infers the nullable form because a nil slice is valid Go, but the handler always builds a slice. Error paths return an error: a tool declaring an OutputSchema MUST return conforming structured content, so a path with no data has to fail. The client compiles every declared OutputSchema at connect time and validates results against it, using jsonschema-go - already an SDK dependency, so no new one. Each channel goes to its stated reader: Content is forwarded to the model, StructuredContent is used as data, reporting how many items came back. The client no longer treats a missing .env as fatal and checks for ANTHROPIC_API_KEY after connecting rather than before, matching the Python and TypeScript clients, so the connection can be exercised without credentials. Requires go-sdk v1.7.0-pre.3: non-object output schema support (SEP-2106) landed after v1.6.1 and is in no stable release. Model identifier moves to claude-sonnet-5; the second call in the tool loop used a hardcoded ModelClaude3_7SonnetLatest while the first used the package variable, so both now use the same one. Note that the SDK sends an array-rooted schema as written on every connection rather than projecting it down, so an older client rejects the tool list. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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| .. | ||
| go.mod | ||
| go.sum | ||
| main.go | ||
| README.md | ||
| weather.exe | ||
A Simple MCP Weather Server written in Go
See the Build an MCP server tutorial for more information.
Building
go build -o weather
Running
./weather
The server will communicate via stdio and expose two MCP tools:
get_forecast- Get weather forecast for a location (requires latitude and longitude)get_alerts- Get weather alerts for a US state (requires two-letter state code)
Structured output
Both tools declare 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 in the spec.
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.