Explain codebase

A skill for mapping and explaining an unfamiliar codebase or module, including its entry points, directories, data flow, and important files.

In plain words
What is it for?
Use it to learn how a project works, trace a representative request or command across files, and find where to make a particular change.
Why use it?
It replaces a broad code dump with a focused explanation grounded in the actual project structure.

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/auravixstudio/caelo/explain-codebase
Any agent
npx skills add AuraVixStudio/caelo --skill explain-codebase
Clone the repo
git clone --depth 1 https://github.com/AuraVixStudio/caelo

Made for: Claude Code, Codex.

Per session 17 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 282 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 $0.00017 $0.00282
Opus 5 $0.00009 $0.00141
Sonnet 5 $0.00003 $0.00056
Haiku 4.5 $0.00002 $0.00028

Measured 2d ago against content hash 033fca0f82f3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

Explain codebase 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.

caelo_core/skills/builtin/explain-codebase/SKILL.md · 28 lines

What it actually says

Explain codebase

Use this when the user wants to understand how a project or module works.

Steps

  1. Orient. Find the entry points, the build/run commands, and any README/architecture docs. Identify the main directories and what each is responsible for.
  2. Trace a path. Pick a representative flow (a request, a command, a feature) and follow it across files. Concrete paths explain a system better than abstractions.
  3. Map the pieces. Note the key modules, the data model, and how components talk to each other (calls, events, HTTP, queues).
  4. Explain. Summarize for the user: the big picture first, then the important components, then the one flow you traced — with clickable file:line references.
  5. Point forward. Call out where to look to change X, and any sharp edges or conventions worth knowing.

Notes

  • Read before asserting. Verify names/paths exist rather than inferring from memory.
  • Tailor depth to the user's question — don't dump the whole tree.
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 · 28 lines · 17 tokens per session scan A 033fca0f82f3

Subscribe to this mod's changes

Explain codebase is a skill published in the GitHub repository AuraVixStudio/caelo (22 stars, last pushed 20d ago), licensed Apache-2.0. It adds 17 tokens to every session and 282 once invoked, about $0.0001 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 2026-08-30.