code-reading

A guide for understanding an unfamiliar, older, or new-to-you codebase. It gives an order for inspecting documentation, dependencies, entry points, data models, user flows, tests, and configuration.

In plain words
What is it for?
Use it when onboarding to a project, investigating legacy code, tracing a feature from trigger to result, or explaining how an existing system works.
Why use it?
It provides a repeatable way to learn how a project works before changing it. Tracing data and execution paths helps reveal responsibilities, external services, dependencies, and failure points.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/jamestorrevillas/dev-skills/code-reading
Any agent
npx skills add jamestorrevillas/dev-skills --skill code-reading
Clone the repo
git clone --depth 1 https://github.com/jamestorrevillas/dev-skills

Made for: Claude Code, Codex.

Per session 66 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 625 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00066 $0.00625
Opus 5 $0.00033 $0.00313
Sonnet 5 $0.00013 $0.00125
Haiku 4.5 $0.00007 $0.00063

Measured 2d ago against content hash 27073639bf70, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

code-reading scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/skills/code-reading/SKILL.md · 84 lines

How it starts

The opening of the file, as written. The whole thing — 84 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Code Reading

Core Principle

Code is read 10x more than it's written. Reading code is a skill you actively develop — not a passive activity.


Codebase Onboarding Order

Always explore a new codebase in this order:

  1. README — What does it do? How do I run it?
  2. Package/dependency files — What tools and frameworks are used?
  3. Entry point — Where does execution start? (main.ts, index.js, app.py)
  4. Core domain models — What are the main data structures?
  5. Key user flows — Trace one important feature end-to-end
  6. Tests — Tests reveal intended behavior and edge cases
  7. Config/env files — What is configurable? What are the environments?

Code Tracing Method

For understanding a specific flow:

1. Start from the trigger (user action, API call, scheduled job)
2. Follow the execution path step by step
3. Note: what data flows in? what comes out?
4. Identify where external systems are called
5. Mark where business logic lives vs. infrastructure

Questions to Ask While Reading

  • What is this component responsible for? (single responsibility check)
  • What does it need to run? (dependencies)
  • What does it produce/return?
  • What could make it fail?
  • Why was it written this way? (check git blame/history for context)

Using AI for Code Reading

"Explain what this function does, including:
- What it takes as input
- What it returns  
- Any side effects
- Non-obvious behavior I should know about"

"Walk me through how [feature] works, 
starting from [entry point] to [output]"

"What would I need to understand to safely 
modify [specific part] of this code?"

  • Search patterns — use grep/ripgrep to find usages of a function/class
  • Git blame — who changed this and why?
  • Git log — when was this introduced? what changed over time?
  • Tests — run tests while reading to see what behavior is expected
  • Dependency graph — which modules depend on what?

Read the full file on GitHub · 84 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 84 lines · 0 tokens per session scan A 27073639bf70

Subscribe to this mod's changes

code-reading is a skill published in the GitHub repository jamestorrevillas/dev-skills (3 stars, last pushed 5mo ago), licensed MIT. It adds 66 tokens to every session and 625 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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