Tool Calling Challenges

Introduction

Sharpen your tool-calling skills: schemas, validation, retries, multi-tool selection, error feedback.

Beginner tip: start with ONE tool; grow only when the first works flawlessly under load.

Understanding the topic

Core concepts:

• Single calculator tool with strict schema.
• Validator that catches every malformed call.
• Retry-with-feedback on tool errors.
• Multi-tool agent (search + calc + DB).
• Tool with auth scoped to a user.
• Idempotent payments tool (Stripe).
• Streaming tool result back into context.
• Confirmation-required destructive tool.
• Tool composition (one tool calls another).
• Tool exposed via MCP server.

Syntax reference

Visual workflow / architecture:

LLM decides
    │
    ▼
{ tool_name, args }
    │
    ▼
┌──────────────┐
│   Validator  │  schema check
└──────┬───────┘
       ▼
┌──────────────┐
│  Tool runner │──► HTTP · DB · Shell
└──────┬───────┘
       │ result
       ▼
   Back to LLM

Real-world use

Every tool-using interview at OpenAI, Anthropic and Cursor tests these.

Best practices

• Schema is a prompt — write it carefully.
• Validate before run; always.

Common mistakes

• Granting destructive tools without confirmation.

Hands-on exercise

Interview preparation — practice these questions:

• Q1. Why does a tool description double as a prompt?
• Q2. Idempotency for payments tools.
• Q3. Scenario: tool fails with cryptic error — how do you make the LLM recover?