codebase-onboarding

codebase-onboarding is a skill for Claude Code, Codex from jxoesneon/Ciel. It costs 25 tokens per session (556 once invoked), scanned A, original, Apache-2.0.

A guided process for understanding an unfamiliar software repository and creating a starter CLAUDE.md file with project-specific instructions. It maps the technology, structure, data flow, and coding conventions.

In plain words
What is it for?
Identifying frameworks and entry points, mapping directories and request flows, finding testing and error-handling conventions, and producing a short onboarding guide.
Why use it?
It reduces the time an agent spends searching through a new codebase and lowers the risk of missing important project patterns.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions CLAUDE.md; mentions subagents.

Good fit Identifying frameworks and entry points, mapping directories and request flows, finding testing and error-handling conventions, and producing a short onboarding guide.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/jxoesneon/ciel/codebase-onboarding
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.

Any agent
npx skills add jxoesneon/Ciel --skill codebase-onboarding
Clone the repo
git clone --depth 1 https://github.com/jxoesneon/Ciel

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for codebase-onboarding

README.md
[![agentmods](https://agentmods.dev/badge/skills/jxoesneon/ciel/codebase-onboarding/github.svg)](https://agentmods.dev/skills/jxoesneon/ciel/codebase-onboarding)
Your own site
<a href="https://agentmods.dev/skills/jxoesneon/ciel/codebase-onboarding"><img src="https://agentmods.dev/badge/skills/jxoesneon/ciel/codebase-onboarding/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for codebase-onboarding

Your own site · 80×15
<a href="https://agentmods.dev/skills/jxoesneon/ciel/codebase-onboarding"><img src="https://agentmods.dev/badge/skills/jxoesneon/ciel/codebase-onboarding.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 25 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 556 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00025 $0.00556
Opus 5 $0.00013 $0.00278
Sonnet 5 $0.00005 $0.00111
Haiku 4.5 $0.00003 $0.00056

Measured 8d ago against content hash df824b1c3309, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, 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 8d 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.

skills/codebase-onboarding/SKILL.md · 61 lines

What it actually says

CIEL ADAPTATION: Codebase Onboarding (Reconnaissance)

This skill is CIEL's entry-point for any new repository. It avoids "reading everything" by using high-signal reconnaissance to build a functional map of the project.

Workflow Phases

Phase 1: Reconnaissance (Parallel)

  • Manifest Detection: Identify the tech stack via package.json, go.mod, Cargo.toml, etc.
  • Framework Fingerprinting: Detect Next.js, Django, FastAPI via config patterns.
  • Entry Point ID: Find main.*, index.*, server.*.
  • Structural Snapshot: Map the top 2 levels of the directory tree.

Phase 2: Architecture Mapping

Define the:

  • Data Flow: Trace a single request from entry (router) to exit (database).
  • Key Directories: Map directories to their semantic purpose (e.g., src/lib -> Shared Utilities).

Phase 3: Convention Detection

Identify existing patterns in:

  • Naming: camelCase vs snake_case.
  • Error Handling: try/catch vs Result types.
  • Testing: Jest vs Pytest, location of test files.

Phase 4: Artifact Generation

  1. Onboarding Guide: A scannable 2-minute summary of the project.
  2. Starter CLAUDE.md: Project-specific instructions and commands for CIEL sub-agents.

Anti-Patterns

  • Context Flooding: Reading the entire src/ directory instead of using glob and grep for reconnaissance.
  • README Redundancy: Copying the project description instead of adding structural and architectural insight.
  • Instruction Over-Engineering: Generating a CLAUDE.md longer than 100 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. 8d ago First seen · 61 lines · 25 tokens per session scan A df824b1c3309

Subscribe to this mod's changes

codebase-onboarding is a skill published in the GitHub repository jxoesneon/Ciel (1 stars, last pushed 4d ago), licensed Apache-2.0. It adds 25 tokens to every session and 556 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 2026-09-03.

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