How to Build an Agent

Source: https://ampcode.com/how-to-build-an-agent Author: Amp Code Date: 2025-07-22

Summary

Practical guide on building a minimal coding agent from scratch. Notable for its minimalism — shows that a capable agent can be built in a surprisingly small amount of code. Clarifies what “agent” actually means at the implementation level.

Key Claims

• Minimal agent = LLM + tool loop: the core of any agent is a loop that calls the model, executes tools from the response, feeds results back.
• The loop is shockingly simple: ~100 lines of Python for a capable coding assistant.
• Tools matter more than model: same model with better tools outperforms same model without tools on most tasks.
• Common mistake: over-engineering the agent architecture before understanding what the model actually needs.
• Key tools for coding agents: read_file, write_file, run_command, search_codebase — these four cover most use cases.
• Debugging agents: add verbose logging of every model call and tool response — the context is your debugging surface.

Concepts

• Coding Agents — minimal implementation guide
• Context Engineering — tool loop is context management