09. Build your own coding agent

Why build one yourself?

Studying agent systems is useful. Building even a small one is where the concepts become real.

A coding agent is a great project because it naturally combines:

• tool calling
• planning loops
• memory
• file operations
• shell execution
• safety controls

Minimal version

A simple coding agent can do this:

1. read task
2. inspect files
3. search relevant code
4. propose or apply edits
5. run validation commands
6. summarize result

That alone already teaches the most important agent ideas.

Minimal architecture

User task
   ↓
Planner / controller
   ↓
Choose tool
   ├── read file
   ├── search files
   ├── edit file
   └── run command
   ↓
Observe result
   ↓
Repeat until task is done

Recommended first tool set

Start with a very small tool set:

• read file
• search files
• write or patch file
• run command
• optional memory / notes tool

Do not begin with too many tools. A smaller system is easier to debug and understand.

Safety basics

Even a personal coding agent should include controls.

Examples:

• ask before destructive file changes
• confirm before shell commands with side effects
• limit accessible directories
• log all tool calls
• cap loop length

These principles matter early.

Suggested milestones

Milestone 1

Build a read-only coding assistant.

Capabilities:

• inspect files
• search project
• explain code

Milestone 2

Add edit capability.

Capabilities:

• suggest patch
• write file
• summarize changes

Milestone 3

Add validation loop.

Capabilities:

• run tests
• read output
• retry or refine fix

Milestone 4

Add memory or project context.

Capabilities:

• remember conventions
• track task progress
• store recurring constraints

Good project ideas

• bug-fix assistant
• test failure investigator
• code explainer with repo search
• documentation updater
• Kubernetes manifest reviewer

Next

After this, continue into the case studies in 03-Advanced/13-Agents/Case-Studies/.