AI SDK Tool Execution Fails After Multiple Messages

The issue you’re experiencing with AI SDK 4 where the model generates JavaScript code but fails to execute tools after multiple messages is a common problem related to tool calling configuration and multi-step execution limits. This behavior typically occurs when the maxSteps parameter isn’t properly configured or when there’s a mismatch between different parts of your tool calling setup.

Contents

• Understanding the maxSteps Parameter
• Common Causes of Tool Execution Failures
• Configuration Best Practices
• Debugging and Troubleshooting
• Migration Considerations

Understanding the maxSteps Parameter

The maxSteps parameter in AI SDK 4.0 controls how many times the model can call tools during a single conversation. When you reach this limit, the model will stop executing tools and instead generate the code as text content.

From the research findings, one Reddit post discovered that when maxSteps values between different components (like useChat and streamText) don’t match, the tools simply don’t execute, causing silent failures.

For your PDF generation scenario, if you’ve configured maxSteps: 4 but the conversation requires more tool calls after the fourth message, the model will generate JavaScript code instead of executing the tool. This explains why the behavior changes on the fifth message.

Common Causes of Tool Execution Failures

1. Mismatched maxSteps Configuration

If you’re using both client-side and server-side tool calling, ensure the maxSteps values match across all components:

// Server-side configuration (your current setup)
return streamText({
    model,
    messages: context,
    tools: getTools(a, b, c, d),
    toolChoice: "auto",
    maxSteps: 10, // Ensure this is sufficient for your use case
    temperature: 0.0,
    abortSignal: abortSignal,
    system: getSystemPrompt(a, b),
});

2. Tool Execution Errors

According to the AI SDK documentation, when tool execution fails, the AI SDK adds them as tool-error content parts to enable automated LLM roundtrips in multi-step scenarios. These errors might be preventing further tool execution.

3. Context Length Limitations

After multiple messages, the conversation context might exceed the model’s token limits, causing it to switch from tool execution to code generation.

Configuration Best Practices

1. Increase maxSteps Appropriately

For complex workflows involving multiple tool calls, set a higher maxSteps value:

return streamText({
    model,
    messages: context,
    tools: getTools(a, b, c, d),
    toolChoice: "auto",
    maxSteps: 20, // Higher value for complex workflows
    maxTokens: 30000,
    temperature: 0.0,
    abortSignal: abortSignal,
    system: getSystemPrompt(a, b),
});

2. Implement Proper Error Handling

Handle tool execution errors gracefully:

const tools = {
    executeJavaScript: tool({
        description: "Execute JavaScript code",
        parameters: z.object({
            code: z.string().describe("The JavaScript code to execute"),
        }),
        execute: async ({ code }) => {
            try {
                // Your execution logic here
                return { result: "Code executed successfully" };
            } catch (error) {
                // Return the error to the model for recovery
                throw new Error(`Execution failed: ${error.message}`);
            }
        },
    }),
};

3. Use Tool Context Properly

Ensure your tools have access to the necessary context:

const tools = {
    createPDF: tool({
        description: "Create a PDF document",
        parameters: z.object({
            content: z.string().describe("The content to include in the PDF"),
        }),
        execute: async ({ content }, context) => {
            // Access conversation history if needed
            const conversationHistory = context.messages;
            // Your PDF creation logic
            return { success: true, pdfId: generatedId };
        },
    }),
};

Debugging and Troubleshooting

1. Check Network Requests

As mentioned in the Microsoft troubleshooting guide, verify that the script defined in the src snippet configuration was downloaded by checking for response code 200 (success) or 304 (not changed) in your network tab.

2. Monitor Tool Execution Flow

Add logging to track tool execution:

const tools = {
    executeJavaScript: tool({
        description: "Execute JavaScript code",
        parameters: z.object({
            code: z.string().describe("The JavaScript code to execute"),
        }),
        execute: async ({ code }) => {
            console.log("Tool execution requested:", code);
            try {
                const result = await executeCode(code);
                console.log("Tool execution successful");
                return result;
            } catch (error) {
                console.error("Tool execution failed:", error);
                throw error;
            }
        },
    }),
};

3. Validate Tool Schemas

Ensure your tool schemas are correctly defined. The research mentions that generateText throws errors for tool schema validation issues, which might prevent execution.

Migration Considerations

The research indicates that AI SDK 5.0 has significant improvements for tool calling. According to the migration guide, the maxSteps parameter has been replaced with stopWhen, which provides more flexible control over multi-step execution.

Key benefits of upgrading to AI SDK 5.0 include:

• Automatic Input Streaming: Tool call inputs now stream by default
• Explicit Error States: Tool execution errors are limited to the tool and can be resubmitted
• Better Multi-step Control: More flexible stop conditions

If you’re experiencing persistent issues with tool execution after multiple messages, consider migrating to AI SDK 5.0 where the tool calling mechanism has been significantly improved.

Sources

1. AI SDK Core: Tool Calling - Official Documentation
2. Migration Guide: AI SDK 4.0 to 5.0
3. Reddit: Vercel AI SDK - Silent Failure with maxSteps
4. AI SDK 5 - Vercel Blog
5. Microsoft Azure Monitor - JavaScript SDK Troubleshooting

Conclusion

The issue where your AI SDK 4 model generates JavaScript code but doesn’t execute tools after multiple messages is most likely caused by either insufficient maxSteps configuration or mismatched parameters between different components.

Key takeaways:

• Ensure your maxSteps value is high enough for your workflow complexity
• Check for consistency between client-side and server-side configurations
• Implement proper error handling and logging for tool execution
• Consider upgrading to AI SDK 5.0 for improved tool calling capabilities

Recommended actions:

1. Increase the maxSteps parameter to handle more tool calls
2. Audit your entire tool calling configuration for parameter mismatches
3. Add comprehensive logging to debug tool execution flow
4. Evaluate migrating to AI SDK 5.0 for better multi-step execution control

By addressing these configuration issues, you should be able to restore proper tool execution behavior even after multiple messages in your conversation.