explain-diff

explain-diff is a skill for Claude Code, Codex from reidemeister94/development-skills. It costs 35 tokens per session (920 once invoked), scanned A, original, MIT.

A guide for explaining a code change, such as a diff, branch, pull request, patch, or review package, to someone without project context. It covers what changed, why it matters, and what was verified.

In plain words
What is it for?
Use it to teach the purpose and effect of a change, walk through related code by concept, explain trade-offs, and report verification gaps.
Why use it?
It makes unfamiliar changes easier to understand and clearly distinguishes observed facts from behavior that has not been checked. It can also explain the underlying technical or business idea.

Skill for Claude CodeCodex

Part of the development-skills plugin — 16 skills, 1 agent, 2 hooks shipped together

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/reidemeister94/development-skills/explain-diff
Any agent
npx skills add reidemeister94/development-skills --skill explain-diff
Clone the repo
git clone --depth 1 https://github.com/reidemeister94/development-skills

Made for: Claude Code, Codex.

Or install development-skills, the plugin that ships this one along with the rest of its 16 skills, 1 agent, 2 hooks.

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 explain-diff

README.md
[![agentmods](https://agentmods.dev/badge/skills/reidemeister94/development-skills/explain-diff.svg)](https://agentmods.dev/skills/reidemeister94/development-skills/explain-diff)
Your own site
<a href="https://agentmods.dev/skills/reidemeister94/development-skills/explain-diff"><img src="https://agentmods.dev/badge/skills/reidemeister94/development-skills/explain-diff.svg" alt="Measured on agentmods" height="20"></a>
Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 920 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 $0.00035 $0.00920
Opus 5 $0.00017 $0.00460
Sonnet 5 $0.00007 $0.00184
Haiku 4.5 $0.00003 $0.00092

Measured 3d ago against content hash bbc88d7dfdff, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

explain-diff 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 3d 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/explain-diff/SKILL.md · 82 lines

How it starts

The opening of the file, as written. The whole thing — 82 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Explain diff

Transfer ownership of a change. Manual mode is repository-read-only; --visual may write only to the system temp directory.

Establish the evidence

Parse --visual; the rest is a working tree, branch, range, PR, patch, or packet. Default to the current worktree. Use the available request, plan, chronicle, verification, and details about what was not checked. Do not require a standard packet.

In Full, require the request, plan or chronicle, diff, fresh Verify results, and details about what was not checked. Otherwise inspect read-only.

State verification status. With absent or stale evidence, label Unverified change and separate code facts from unproved behavior.

For --visual, read visual mode. At the automatic Full checkpoint, name the dynamic concept a visual would clarify and ask Continue in chat or Create visual; only the latter activates it.

Teach the change

Assume no project knowledge. Present only what the change needs:

  1. the minimum background and vocabulary needed;
  2. the intuition and functional result;
  3. concrete examples or sanitized toy data;
  4. a guided diff ordered by concept, not file order;
  5. decisions, trade-offs, failure modes, and evidence limits;
  6. the comprehension dialogue below.

Use a small diagram only when clearer than prose.

Check understanding

Merge overlapping concepts and omit filler. Zero questions is valid. Cover relevant business rules, invariants, flows, states, edge cases, architecture, lifecycle, concurrency, trade-offs, failure modes, and evidence—not syntax.

Ask one applied free-response question at a time through AskUserQuestion. Show the text box with I don't know — explain and Proceed without answering, translated to the conversation language. Do not offer answer choices. In the question text, invite the user to answer in the free-text box; never name interface internals such as "Other".

If the interface cannot show selectable actions, list those two actions beside the free-response prompt.

Read the full file on GitHub · 82 lines

Files

What ships with it

1 file 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. 3d ago First seen · 82 lines · 35 tokens per session scan A bbc88d7dfdff

Subscribe to this mod's changes

explain-diff is a skill published in the GitHub repository reidemeister94/development-skills (11 stars, last pushed 1mo ago), licensed MIT. It adds 35 tokens to every session and 920 once invoked, about $0.0002 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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