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all: add examples of customizing tool schemas, and clarify documentation (#421)

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Add example/server/toolschemas, which demonstrates various ways to
customize tool schemas, and illustrates the differences between
ToolHandler and ToolHandlerFor.

Fixes #385
Fixes #386
For #368
This commit is contained in:
Robert Findley 2025-09-05 14:11:11 -04:00 • committed by GitHub
commit 40b6bd30f1
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1 changed files with 309 additions and 100 deletions
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39
mcp/protocol.go
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@ -49,7 +49,9 @@ type CallToolParams struct {
Arguments any `json:"arguments,omitempty"`
}
// CallToolParamsRaw is passed to tool handlers on the server.
// CallToolParamsRaw is passed to tool handlers on the server. Its arguments
// are not yet unmarshaled (hence "raw"), so that the handlers can perform
// unmarshaling themselves.
type CallToolParamsRaw struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
@ -58,29 +60,48 @@ type CallToolParamsRaw struct {
Arguments json.RawMessage `json:"arguments,omitempty"`
}
// The server's response to a tool call.
// A CallToolResult is the server's response to a tool call.
//
// The [ToolHandler] and [ToolHandlerFor] handler functions return this result,
// though [ToolHandlerFor] populates much of it automatically as documented at
// each field.
type CallToolResult struct {
// This property is reserved by the protocol to allow clients and servers to
// attach additional metadata to their responses.
Meta `json:"_meta,omitempty"`
// A list of content objects that represent the unstructured result of the tool
// call.
//
// When using a [ToolHandlerFor] with structured output, if Content is unset
// it will be populated with JSON text content corresponding to the
// structured output value.
Content []Content `json:"content"`
// An optional JSON object that represents the structured result of the tool
// call.
// StructuredContent is an optional value that represents the structured
// result of the tool call. It must marshal to a JSON object.
//
// When using a [ToolHandlerFor] with structured output, you should not
// populate this field. It will be automatically populated with the typed Out
// value.
StructuredContent any `json:"structuredContent,omitempty"`
// Whether the tool call ended in an error.
// IsError reports whether the tool call ended in an error.
//
// If not set, this is assumed to be false (the call was successful).
//
// Any errors that originate from the tool should be reported inside the result
// object, with isError set to true, not as an MCP protocol-level error
// response. Otherwise, the LLM would not be able to see that an error occurred
// and self-correct.
// Any errors that originate from the tool should be reported inside the
// Content field, with IsError set to true, not as an MCP protocol-level
// error response. Otherwise, the LLM would not be able to see that an error
// occurred and self-correct.
//
// However, any errors in finding the tool, an error indicating that the
// server does not support tool calls, or any other exceptional conditions,
// should be reported as an MCP error response.
//
// When using a [ToolHandlerFor], this field is automatically set when the
// tool handler returns an error, and the error string is included as text in
// the Content field.
IsError bool `json:"isError,omitempty"`
}