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all: add examples of customizing tool schemas, and clarify documentation #421
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,146 @@ | ||
| // Copyright 2025 The Go MCP SDK Authors. All rights reserved. | ||
| // Use of this source code is governed by an MIT-style | ||
| // license that can be found in the LICENSE file. | ||
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| // The toolschemas example demonstrates how to create tools using both the | ||
| // low-level [ToolHandler] and high level [ToolHandlerFor], as well as how to | ||
| // customize schemas in both cases. | ||
| package main | ||
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| import ( | ||
| "context" | ||
| "encoding/json" | ||
| "fmt" | ||
| "log" | ||
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| "github.com/google/jsonschema-go/jsonschema" | ||
| "github.com/modelcontextprotocol/go-sdk/mcp" | ||
| ) | ||
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| // Input is the input into all the tools handlers below. | ||
| type Input struct { | ||
| Name string `json:"name" jsonschema:"the person to greet"` | ||
| } | ||
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| // Output is the structured output of the tool. | ||
| // | ||
| // Not every tool needs to have structured output. | ||
| type Output struct { | ||
| Greeting string `json:"greeting" jsonschema:"the greeting to send to the user"` | ||
| } | ||
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| // simpleGreeting is an [mcp.ToolHandlerFor] that only cares about input and output. | ||
| func simpleGreeting(_ context.Context, _ *mcp.CallToolRequest, input Input) (*mcp.CallToolResult, Output, error) { | ||
| return nil, Output{"Hi " + input.Name}, nil | ||
| } | ||
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| // manualGreeter handles the parsing and validation of input and output manually. | ||
| // | ||
| // Therfore, it needs to close over its resolved schemas, to use them in | ||
| // validation. | ||
| type manualGreeter struct { | ||
| inputSchema *jsonschema.Resolved | ||
| outputSchema *jsonschema.Resolved | ||
| } | ||
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| func (t *manualGreeter) greet(_ context.Context, req *mcp.CallToolRequest) (*mcp.CallToolResult, error) { | ||
| // errf produces a 'tool error', embedding the error in a CallToolResult. | ||
| errf := func(format string, args ...any) *mcp.CallToolResult { | ||
| return &mcp.CallToolResult{ | ||
| Content: []mcp.Content{&mcp.TextContent{Text: fmt.Sprintf(format, args...)}}, | ||
| IsError: true, | ||
| } | ||
| } | ||
| // Handle the parsing and validation of input and output. | ||
| // | ||
| // Note that errors here are treated as tool errors, not protocol errors. | ||
| var input Input | ||
| if err := json.Unmarshal(req.Params.Arguments, &input); err != nil { | ||
| return errf("failed to unmarshal arguments: %v", err), nil | ||
| } | ||
| if err := t.inputSchema.Validate(input); err != nil { | ||
| return errf("invalid input: %v", err), nil | ||
| } | ||
| output := Output{Greeting: "Hi " + input.Name} | ||
| if err := t.outputSchema.Validate(output); err != nil { | ||
| return errf("tool produced invalid output: %v", err), nil | ||
| } | ||
| outputJSON, err := json.Marshal(output) | ||
| if err != nil { | ||
| return errf("output failed to marshal: %v", err), nil | ||
| } | ||
| return &mcp.CallToolResult{ | ||
| Content: []mcp.Content{&mcp.TextContent{Text: string(outputJSON)}}, | ||
| StructuredContent: output, | ||
| }, nil | ||
| } | ||
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| func main() { | ||
| server := mcp.NewServer(&mcp.Implementation{Name: "greeter"}, nil) | ||
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| // Add the 'greeting' tool in a few different ways. | ||
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| // First, we can just use [mcp.AddTool], and get the out-of-the-box handling | ||
| // it provides: | ||
| mcp.AddTool(server, &mcp.Tool{Name: "simple greeting"}, simpleGreeting) | ||
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| // Next, we can create our schemas entirely manually, and add them using | ||
| // [mcp.Server.AddTool]. Since we're working manually, we can add some | ||
| // constraints on the length of the name. | ||
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| // | ||
| // We don't need to do all this work: below, we use jsonschema.For to start | ||
| // from the default schema. | ||
| var ( | ||
| manual manualGreeter | ||
| err error | ||
| ) | ||
| inputSchema := &jsonschema.Schema{ | ||
| Type: "object", | ||
| Properties: map[string]*jsonschema.Schema{ | ||
| "name": {Type: "string", MaxLength: jsonschema.Ptr(10)}, | ||
| }, | ||
| } | ||
| manual.inputSchema, err = inputSchema.Resolve(nil) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| outputSchema := &jsonschema.Schema{ | ||
| Type: "object", | ||
| Properties: map[string]*jsonschema.Schema{ | ||
| "greeting": {Type: "string"}, | ||
| }, | ||
| } | ||
| manual.outputSchema, err = outputSchema.Resolve(nil) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| server.AddTool(&mcp.Tool{ | ||
| Name: "manual greeting", | ||
| InputSchema: inputSchema, | ||
| OutputSchema: outputSchema, | ||
| }, manual.greet) | ||
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| // Finally, note that we can also use custom schemas with a ToolHandlerFor. | ||
| // We can do this in two ways: by using one of the schema values constructed | ||
| // above, or by using jsonschema.For and adjusting the resulting schema. | ||
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| mcp.AddTool(server, &mcp.Tool{ | ||
| Name: "customized greeting 1", | ||
| InputSchema: inputSchema, | ||
| // OutputSchema will still be derived from Output. | ||
| }, simpleGreeting) | ||
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| customSchema, err := jsonschema.For[Input](nil) | ||
| if err != nil { | ||
| log.Fatal(err) | ||
| } | ||
| customSchema.Properties["name"].MaxLength = jsonschema.Ptr(10) | ||
| mcp.AddTool(server, &mcp.Tool{ | ||
| Name: "customized greeting 2", | ||
| InputSchema: customSchema, | ||
| }, simpleGreeting) | ||
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| // Now run the server. | ||
| if err := server.Run(context.Background(), &mcp.StdioTransport{}); err != nil { | ||
| log.Printf("Server failed: %v", err) | ||
| } | ||
| } | ||
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