Building Your Own Agents

Beyond using Claude Code as your agent, you can build your own agents using the Claude Agent SDK. This lets you create specialized AI tools for specific workflows.

What Is an Agent?

An agent is a program that:

1. Takes a goal or task
2. Plans how to achieve it
3. Uses tools to take actions
4. Loops until the task is complete

Claude Code itself is an agent. The Agent SDK lets you build similar systems for your own use cases.

The Claude Agent SDK

The Agent SDK provides the building blocks:

npm install claude-agent-sdk

Basic Agent Structure

import { Agent, tool } from 'claude-agent-sdk';

const agent = new Agent({
  model: 'claude-sonnet-4-6',
  instructions: 'You are a helpful code review agent.',
  tools: [
    tool({
      name: 'read_file',
      description: 'Read a file from the repository',
      parameters: { path: { type: 'string' } },
      execute: async ({ path }) => {
        return fs.readFileSync(path, 'utf-8');
      },
    }),
    tool({
      name: 'list_files',
      description: 'List files in a directory',
      parameters: { directory: { type: 'string' } },
      execute: async ({ directory }) => {
        return fs.readdirSync(directory).join('\n');
      },
    }),
  ],
});

const result = await agent.run('Review the src/ directory for security issues');
console.log(result);

Use Cases for Custom Agents

Specialized Code Review Agent

An agent that knows your team’s specific code standards and can review PRs against them.

Content Migration Agent

An agent that reads from one CMS (WordPress) and writes to another (Astro markdown files), handling format conversion.

Monitoring Agent

An agent that checks your services, analyzes logs, and creates incident reports.

Data Processing Agent

An agent that reads CSV/JSON data, cleans it, transforms it, and loads it into your database.

Agent vs. Skill vs. Script

	Agent	Skill	Script
Intelligence	AI-powered decisions	AI executes a prompt	Fixed logic
Flexibility	Adapts to situations	Follows instructions	Follows code
Complexity	Can handle ambiguity	Structured workflows	Deterministic
When to use	Novel, variable tasks	Repeatable workflows	Known, fixed logic

When to Build an Agent

Build a custom agent when:

• The task requires AI judgment (not just following steps)
• Claude Code is too general for your specific domain
• You need to distribute the tool to others
• You want to run it in CI/CD or on a schedule

Exercise

1. Identify a repetitive task that requires judgment
2. List the tools the agent would need
3. Define the agent’s instructions
4. Build a simple version with the Agent SDK
5. Test it on real data and iterate