codebase-explorer

A guide for understanding an unfamiliar part of a codebase by tracing a feature, domain, or data flow. A codebase is the complete collection of source files that make up an application.

In plain words
What is it for?
Use it to investigate questions such as how authentication works, what happens when a user buys something, or where a business domain is implemented.
Why use it?
It helps answer how a feature works end to end without confusing broad conceptual questions with precise questions about one symbol or function.

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/kouroshez/coding-os/codebase-explorer
Any agent
npx skills add kouroshez/coding-os --skill codebase-explorer
Clone the repo
git clone --depth 1 https://github.com/kouroshez/coding-os

Made for: Claude Code, Codex.

Per session 92 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 887 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 $0.00092 $0.00887
Opus 5 $0.00046 $0.00443
Sonnet 5 $0.00018 $0.00177
Haiku 4.5 $0.00009 $0.00089

Measured yesterday against content hash 7d8aa2428e24, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

codebase-explorer 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 yesterday.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/outline.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

src/core/skills/codebase-explorer/SKILL.md · 90 lines

How it starts

The opening of the file, as written. The whole thing — 90 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Explore the specified conceptual area of the codebase and produce a structured map. Boundary with graph-explorer:

Question shape Use
"How does X work end-to-end?" codebase-explorer
"What happens when a user does Y?" codebase-explorer
"Where does this domain live?" codebase-explorer
"What calls function foo?" graph-explorer (cos_graph_references)
"What breaks if I rename Bar?" graph-explorer (cos_graph_rename_plan)
"Blast radius of changing baz?" graph-explorer (cos_graph_impact)

codebase-explorer always consults graph-explorer for symbol-precise sub-questions during a conceptual walk — they compose, they don't compete.

Process

  1. Graph gate — If the query is an identifier-shaped symbol (camelCase, snake_case, Class.method, TASK-NNN, dotted path), try cos_graph_query first. It is faster + more accurate than grep for named symbols AND returns confidence-scored edges. Fall back to grep only if the graph returns zero hits (fresh repo, unindexed file) or the query is conceptual ("auth flow", "money handling").
  2. Entry points — Use Grep to find the main files related to the topic.
  3. Trace the flow — Read key files, follow imports. When symbols cross file boundaries, prefer cos_graph_context(uid, depth=1) over chasing imports by hand — it returns the neighbourhood in a single MCP call.
  4. Dependencies — Identify what this area depends on (models, services, external APIs). For impact analysis, use cos_graph_impact(uid, direction="downstream") — the plan's Formula-2 Step-10 tool.
  5. Test coverage — Use Glob to find related test files. Graph edges of type tested_by (when present) point directly at them.

Output Format

Return a structured summary:

## [Area Name] — Codebase Map

### Entry Points
- file:line — description

### Data Flow
source → transform → destination

### Key Files
- path — responsibility

### Dependencies
- internal: models, services used
- external: APIs, packages

### Test Coverage
- test files found
- gaps identified

### Risks
- anything fragile, tightly coupled, or undocumented

Read the full file on GitHub · 90 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. yesterday First seen · 90 lines · 92 tokens per session scan A 7d8aa2428e24

Subscribe to this mod's changes

codebase-explorer is a skill published in the GitHub repository kouroshez/coding-os (6 stars, last pushed yesterday), licensed Apache-2.0. It adds 92 tokens to every session and 887 once invoked, about $0.0005 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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