Assist code understanding

Introduction

This practice helps developers understand unfamiliar or legacy code faster by using coding assistants to explain intent, data flow, dependencies, assumptions, and likely failure modes. It is especially valuable for onboarding engineers, maintainers of legacy systems, and reviewers who need to assess impact quickly. The assistant should be used as a guided reading companion: it accelerates analysis and reduces cognitive load, but human validation remains essential for correctness, security, and final interpretation.

Use targeted excerpts, relevant context, and concrete questions to obtain useful explanations. Strong outputs can then be turned into lightweight documentation, onboarding notes, or design-review support, provided they are checked against the actual code, tests, and runtime behavior.

Key principles

• Start from a narrow scope. Use a focused function, class, or module instead of a whole file to reduce noise and improve precision.
• Ask structured, explicit questions. Request intent, assumptions, edge cases, risks, or a traced walkthrough on a concrete input rather than a vague summary.
• Ground explanations in evidence. Provide relevant tests, logs, expected behavior, or domain rules so the assistant can reason with context.
• Use AI to surface uncertainties, not to replace judgment. The real value is uncovering hidden assumptions, side effects, and missing validations that you then verify manually.
• Capture reusable insights. When an explanation is helpful, convert it into concise documentation for onboarding or future maintenance.

Examples

• Understand a legacy function. Select a function and ask the assistant to explain its intent, list assumptions, and walk through a real input step by step. This is useful before fixing a bug or making a change in unfamiliar code.
• Investigate a failing behavior. Provide a failing test name, stack trace, or log excerpt and ask the assistant to map it to the relevant code path, highlight potential causes, and suggest what to inspect next.
• Create onboarding documentation. After a validated explanation, ask the assistant to draft a short README section or docstring for a new joiner, then review it against the real entry points, tests, and naming conventions.

Drawbacks / anti-patterns

• Sending overly large or unsanitized code, which increases noise, drift, and confidentiality risk.
• Asking vague questions such as “explain this code” without stating the goal, expected level of detail, or relevant context.
• Treating the assistant’s explanation as a substitute for debugging, review, or design judgment.
• Accepting reasoning without verifying assumptions, edge cases, and actual runtime behavior.
• Letting the discussion drift into unsolicited redesign or architecture changes when the goal is simply to understand existing code.