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Tool calling and actions

Day 12 of 30 · Generative AI 2026: Build AI Apps and Agents

One-liner: Connect the model to tools and enforce safe actions.
Time: 20 to 30 min
Deliverable: Tool Schema and Action Example

Learning goal

You will be able to: Define a tool schema and run a safe tool call.

Success criteria (observable)

  • Tool schema includes name, inputs, and output shape.
  • The tool call runs with a real example.
  • Unsafe actions are blocked.

Output you will produce

  • Deliverable: Tool Schema and Action Example
  • Format: JSON schema plus test log
  • Where saved: Repo and course folder notes

Who

Primary persona: Digital nomad building tool enabled AI features Secondary persona(s): Users who trigger actions Stakeholders (optional): Collaborators

What

What it is

A tool definition that tells the model what it can call and how. A small example that proves the tool call works as intended.

What it is not

It is not a full automation platform or a permission system. It is a controlled first step to reliable actions.

2-minute theory

  • Tool calling makes AI useful beyond text output.
  • Clear schemas reduce errors and unexpected inputs.
  • Guardrails prevent unsafe or unintended actions.

Key terms

  • Tool schema: A structured definition of inputs and outputs.
  • Guardrail: A rule that blocks unsafe actions.

Where

Applies in

  • Agent workflows
  • Backend services

Does not apply in

  • Static content generation only

Touchpoints

  • Tool definitions
  • Action logs
  • Permission checks

When

Use it when

  • You want the AI to trigger actions
  • You need predictable inputs

Frequency

Whenever you add a new tool

Late signals

  • Tool calls fail with bad inputs
  • Unexpected actions occur

Why it matters

Practical benefits

  • More useful AI features
  • Fewer failures in automation
  • Better safety and trust

Risks of ignoring

  • Broken workflows
  • Unsafe actions

Expectations

  • Improves: reliability and safety
  • Does not guarantee: perfect decisions

How

Step-by-step method

  1. Define the tool name and purpose.
  2. Specify input fields and types.
  3. Define the output shape.
  4. Add guardrails for unsafe actions.
  5. Run a test call and log results.

Do and don't

Do

  • Validate inputs before execution
  • Log every action

Don't

  • Allow tools to run without checks
  • Expose dangerous actions by default

Common mistakes and fixes

  • Mistake: Loose schema. Fix: Add required fields and types.
  • Mistake: No guardrails. Fix: Block unsafe parameters.

Done when

  • Tool schema is defined and tested.
  • Guardrails block unsafe inputs.
  • Logs show a successful call.

Guided exercise (10 to 15 min)

Inputs

  • One tool idea
  • Example input values

Steps

  1. Write the tool schema.
  2. Add guardrails for unsafe inputs.
  3. Run a test call and log the output.

Output format

Field Value
Tool name
Input schema
Guardrails
Test result

Pro tip: If a tool can change data, add a confirmation step.

Independent exercise (5 to 10 min)

Task

Add one additional guardrail and rerun the test.

Output

Updated schema and test log.

Self-check (yes/no)

  • Is the schema explicit and typed?
  • Are unsafe actions blocked?
  • Is a test call recorded?
  • Are logs stored?

Baseline metric (recommended)

  • Score: 1 tool call succeeds with guardrails
  • Date: 2026-02-06
  • Tool used: Notes app

Bibliography (sources used)

  1. OpenAI Tools Guide. OpenAI. 2026-02-06. Read: https://platform.openai.com/docs/guides/tools

  2. OWASP API Security Top 10. OWASP. 2024-01-01. Read: https://owasp.org/www-project-api-security/

Read more (optional)

  1. Function Calling Best Practices Why: Safe patterns for tool calling. Read: https://platform.openai.com/docs/guides/tools