Method AddTool

mcp/server.go:238–283

AddTool adds a [Tool] to the server, or replaces one with the same name. The Tool argument must not be modified after this call. The tool's input schema must be non-nil and have the type "object". For a tool that takes no input, or one where any input is valid, set [Tool.InputSchema] to `{"type": "

(t *Tool, h ToolHandler)

// Most users should use the top-level function [AddTool], which handles all these
// responsibilities.
func (s *Server) AddTool(t *Tool, h ToolHandler) {
	if err := validateToolName(t.Name); err != nil {
		s.opts.Logger.Error(fmt.Sprintf("AddTool: invalid tool name %q: %v", t.Name, err))
	}
	if t.InputSchema == nil {
		// This prevents the tool author from forgetting to write a schema where
		// one should be provided. If we papered over this by supplying the empty
		// schema, then every input would be validated and the problem wouldn't be
		// discovered until runtime, when the LLM sent bad data.
		panic(fmt.Errorf("AddTool %q: missing input schema", t.Name))
	}
	if s, ok := t.InputSchema.(*jsonschema.Schema); ok {
		if s.Type != "object" {
			panic(fmt.Errorf(`AddTool %q: input schema must have type "object"`, t.Name))
		}
	} else {
		var m map[string]any
		if err := remarshal(t.InputSchema, &m); err != nil {
			panic(fmt.Errorf("AddTool %q: can't marshal input schema to a JSON object: %v", t.Name, err))
		}
		if typ := m["type"]; typ != "object" {
			panic(fmt.Errorf(`AddTool %q: input schema must have type "object" (got %v)`, t.Name, typ))
		}
	}
	if t.OutputSchema != nil {
		if s, ok := t.OutputSchema.(*jsonschema.Schema); ok {
			if s.Type != "object" {
				panic(fmt.Errorf(`AddTool %q: output schema must have type "object"`, t.Name))
			}
		} else {
			var m map[string]any
			if err := remarshal(t.OutputSchema, &m); err != nil {
				panic(fmt.Errorf("AddTool %q: can't marshal output schema to a JSON object: %v", t.Name, err))
			}
			if typ := m["type"]; typ != "object" {
				panic(fmt.Errorf(`AddTool %q: output schema must have type "object" (got %v)`, t.Name, typ))
			}
		}
	}
	st := &serverTool{tool: t, handler: h}
	// Assume there was a change, since add replaces existing tools.
	// (It's possible a tool was replaced with an identical one, but not worth checking.)
	// TODO: Batch these changes by size and time? The typescript SDK doesn't.
	// TODO: Surface notify error here? best not, in case we need to batch.
	s.changeAndNotify(notificationToolListChanged, func() bool { s.tools.add(st); return true })
}

func toolForErr[In, Out any](t *Tool, h ToolHandlerFor[In, Out], cache *SchemaCache) (*Tool, ToolHandler, error) {
	tt := *t