# Ask before running a tool

> Pause a tool call until a user approves it, with signed approval requests and the useChat round trip.

Canonical URL: https://goaisdk.com/docs/recipes/tool-approval
Documentation index: https://goaisdk.com/llms.txt

Let the model request a tool, but run it only after the user says yes.

```go
package main

import (
	"context"
	"crypto/rand"
	"encoding/json"
	"log"
	"net/http"
	"os"
	"time"

	"github.com/digitallysavvy/go-ai/pkg/agent"
	"github.com/digitallysavvy/go-ai/pkg/ai"
	"github.com/digitallysavvy/go-ai/pkg/provider/types"
	"github.com/digitallysavvy/go-ai/pkg/providers/anthropic"
	"github.com/digitallysavvy/go-ai/pkg/schema"
)

func main() {
	model, err := anthropic.New(anthropic.Config{APIKey: os.Getenv("ANTHROPIC_API_KEY")}).
		LanguageModel(anthropic.ClaudeSonnet5_5)
	if err != nil {
		log.Fatal(err)
	}

	// Signs approval requests so a client cannot forge an approval. Use a
	// stable secret in production, the same on every instance.
	secret := []byte(os.Getenv("TOOL_APPROVAL_SECRET"))
	if len(secret) == 0 {
		secret = make([]byte, 32)
		if _, err := rand.Read(secret); err != nil {
			log.Fatal(err)
		}
	}

	deploy := types.Tool{
		Name:        "deploy",
		Description: "Deploy the service to an environment. Requires user approval.",
		Parameters: schema.NewSimpleJSONSchema(map[string]interface{}{
			"type": "object",
			"properties": map[string]interface{}{
				"env": map[string]interface{}{"type": "string", "enum": []string{"staging", "prod"}},
			},
			"required": []string{"env"},
		}),
		// The model can ask; only the user can say yes.
		ToolApproval: true,
		Execute: func(ctx context.Context, input map[string]interface{}, opts types.ToolExecutionOptions) (interface{}, error) {
			return map[string]interface{}{"deployed": input["env"]}, nil
		},
	}

	assistant := agent.NewToolLoopAgent(agent.AgentConfig{
		Model:                          model,
		System:                         "You deploy services. Call deploy when asked. Keep replies short.",
		Tools:                          []types.Tool{deploy},
		StopWhen:                       []ai.StopCondition{ai.IsStepCount(5)},
		ExperimentalToolApprovalSecret: secret,
	})

	http.HandleFunc("POST /api/chat", func(w http.ResponseWriter, r *http.Request) {
		var req struct {
			Messages json.RawMessage `json:"messages"`
		}
		if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 8<<20)).Decode(&req); err != nil {
			http.Error(w, "invalid request body", http.StatusBadRequest)
			return
		}
		chunks, _, err := agent.CreateAgentUIStreamFromUIMessages(r.Context(), assistant,
			agent.CreateAgentUIStreamFromUIMessagesOptions{UIMessages: []byte(req.Messages)})
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}
		keepAlive := 15 * time.Second
		if err := ai.PipeUIMessageChunksToResponse(chunks, w, &ai.UIMessageStreamResponseInit{KeepAliveMs: &keepAlive}); err != nil {
			log.Printf("write stream: %v", err)
		}
	})

	log.Println("listening on :8080")
	log.Fatal(http.ListenAndServe(":8080", nil))
}
```

Run it:

```bash
ANTHROPIC_API_KEY=... go run ./examples/recipes/tool-approval
```

## Notes

- `ToolApproval: true` on the tool makes the agent stop and send an approval request instead of running it.
- `ExperimentalToolApprovalSecret` signs each request. The server verifies the signature when the approval comes back, so a client cannot forge one.
- The client needs `addToolApprovalResponse` and `sendAutomaticallyWhen: lastAssistantMessageIsCompleteWithApprovalResponses`.
- To ask only sometimes, set `ToolApproval` to a `types.ToolNeedsApprovalFunc`. Values the SDK doesn't recognize fail closed: the tool reports an error instead of running.

## Go deeper

- [Guide: Tool approval end to end](https://goaisdk.com/docs/build-a-chat-app/tool-approval.md)
- [Reference: Tool](https://goaisdk.com/docs/reference/ai/tool.md)
- [Guide: Building agents](https://goaisdk.com/docs/agents/building-agents.md)

The full program is at [`examples/recipes/tool-approval/main.go`](https://github.com/digitallysavvy/go-ai/blob/main/examples/recipes/tool-approval/main.go).