code-understand

A codebase analysis tool that maps the files and named pieces of code an application's design depends on, with source locations and supporting evidence.

In plain words
What is it for?
Use it to understand an unfamiliar module, trace who uses a function, identify important files, or estimate the impact of a set of changes.
Why use it?
It reduces the need to search through unfamiliar code at random. It helps reveal what may be affected before you edit, refactor, or investigate how something works.

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/ar9av/obsidian-wiki/code-understand
Any agent
npx skills add Ar9av/obsidian-wiki --skill code-understand
Clone the repo
git clone --depth 1 https://github.com/Ar9av/obsidian-wiki

Made for: Claude Code, Codex.

Per session 175 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,221 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 $0.00175 $0.01221
Opus 5 $0.00088 $0.00611
Sonnet 5 $0.00035 $0.00244
Haiku 4.5 $0.00017 $0.00122

Measured today against content hash 28fff0aaa027, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

code-understand 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 today.

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/code-understand/SKILL.md · 91 lines

How it starts

The opening of the file, as written. The whole thing — 91 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Code Understand — On-Demand Architecture Focus Map

You are about to work in a codebase you don't fully know yet. Instead of grepping around or reading files at random, ask the local extractor for a focus map: the ranked symbols the architecture hangs on, each with a file:line citation and evidence type. Read only what it points at — this is a map, not a substitute for reading the actual code it cites.

When to reach for this

  • Before editing an unfamiliar module — see what calls it and what it calls before changing its shape.
  • The user asks "how does X work", "what's the impact of changing Y", "who else uses this function" for a codebase, not the wiki.
  • You're about to do a large refactor and want a ranked list of load-bearing files instead of reading the whole tree.
  • You already have a diff or a set of changed files and want to know their blast radius before finishing the change.

Not for: summarizing what a project does for the wiki (that's wiki-update Step 3b, which calls this same command as part of a bigger sync flow) — use this skill directly only when you need the focus map for your own immediate work, not to persist knowledge.

Running it

obsidian-wiki code-understand --project <dir> [--backend auto|builtin|codegraph] \
    [--changed <file>...] [--since <sha>] [--max-symbols N] [--pretty]
  • --project — defaults to the current directory.
  • No --changed/--since — seeds from every tracked file (full-project scan).
  • --changed <file> (repeatable) — seed from specific files you already know are relevant (e.g. files in the diff you're about to make).
  • --since <sha> — seed from everything changed since a git ref (e.g. --since HEAD~5 or a base branch).
  • --backendauto (default) uses CodeGraph when installed, falls back to the builtin extractor otherwise; force builtin for the dependency-free path, or codegraph to require the enhanced backend (fails loudly if it's not installed rather than silently degrading).
  • --max-symbols — cap the focus map size (default 50); keep this small for a quick orientation pass, raise it for a thorough one.

Read the full file on GitHub · 91 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. today Changed 28fff0aaa027
  2. yesterday First seen · 91 lines · 175 tokens per session scan A 3d37f30d1ca4

Subscribe to this mod's changes

code-understand is a skill published in the GitHub repository Ar9av/obsidian-wiki (3,325 stars, last pushed today), licensed MIT. It adds 175 tokens to every session and 1,221 once invoked, about $0.0009 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.

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