codebase-onboarding

A first-day guide to an unfamiliar software repository, including its structure, important files, frequently changed areas, and contributors.

In plain words
What is it for?
Use it when joining a team or starting work in an unknown repository and needing an overview of the product, key code paths, ownership, and project-specific rules.
Why use it?
It reduces the time a new engineer spends guessing how the codebase works and who understands each part. A repository is the project’s files and history, while a codebase is the complete body of its source code.

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/dhevenddra/forensic-deepdive/codebase-onboarding
Any agent
npx skills add Dhevenddra/forensic-deepdive --skill codebase-onboarding
Clone the repo
git clone --depth 1 https://github.com/Dhevenddra/forensic-deepdive

Made for: Claude Code, Codex.

Per session 139 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 655 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 $0.00139 $0.00655
Opus 5 $0.00069 $0.00328
Sonnet 5 $0.00028 $0.00131
Haiku 4.5 $0.00014 $0.00065

Measured 2d ago against content hash ded54fbf4d79, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

codebase-onboarding 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.

tests/fixtures/prior_release/v0_8_0/.claude/skills/codebase-onboarding/SKILL.md · 38 lines

What it actually says

Codebase onboarding

The first-day brief. One pass through all five artifacts, ordered for a new engineer.

When to use

  • User explicitly signals they are new to this codebase / team.
  • Question shape: 'onboard me', 'what should I know', 'give me the first-day brief', 'I'm new here'.

When NOT to use

  • User has a specific task (bug, feature, refactor) → use the targeted skill.
  • User is mid-task and asks a focused question → use codebase-exploring or codebase-debugging.

How to answer — read in this order

  1. docs/codebase/AGENT_BRIEF.md (≤ 5 KB) — the never/always rules, the load-bearing symbol, the coupling rules. This is the floor; everything else is depth.
  2. docs/codebase/MENTAL_MODEL.md — entry points, layers, domains. The 'what is this product' answer.
  3. docs/codebase/MAP.md — most central files, key definitions. Where the weight is.
  4. docs/codebase/HOTPATHS.md — hot spots, cross-file dependencies, churn × centrality. What's actively changing.
  5. docs/codebase/ARCHAEOLOGY.md — top contributors with share %, bus factor, recent commits. Who to ask about what.

Surface ownership

After the read-through, name the top 3 contributors by share % from ARCHAEOLOGY.md and what they own (most-touched files). Bus-factor warnings go up front. A new engineer needs to know whose code they're about to step on.

Citation rule

Cite every artifact line: docs/codebase/AGENT_BRIEF.md:12, docs/codebase/ARCHAEOLOGY.md:34. The brief should be navigable, not a paraphrase.

What to report back

  • One-paragraph 'what is this product' summary from MENTAL_MODEL.
  • 5 named load-bearing files with one-line descriptions from MAP.
  • Top 3 contributors with share % and the files they own from ARCHAEOLOGY.
  • Every 'Always' rule from docs/codebase/AGENT_BRIEF.md, verbatim.
  • Suggested next-step skill: 'for a specific bug, switch to codebase-debugging; for a change, codebase-impact-analysis.'
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 · 38 lines · 139 tokens per session scan A ded54fbf4d79

Subscribe to this mod's changes

codebase-onboarding is a skill published in the GitHub repository Dhevenddra/forensic-deepdive (2 stars, last pushed 17d ago), licensed Apache-2.0. It adds 139 tokens to every session and 655 once invoked, about $0.0007 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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