diff-review

A focused code-review guide for an exact diff, patch, branch, commit, or pull request. It looks for correctness defects, missed requirements, missing tests, and regression risks in the changed code.

In plain words
What is it for?
Use it for pre-merge reviews, self-reviews, checking specification compliance, identifying test gaps, and assessing regression risk.
Why use it?
It keeps the review tied to the proposed change and its specification, making findings easier to reproduce while avoiding unrelated whole-project audits.

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/fmind/dotfiles/diff-review
Any agent
npx skills add fmind/dotfiles --skill diff-review
Clone the repo
git clone --depth 1 https://github.com/fmind/dotfiles

Made for: Claude Code, Codex.

Per session 57 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,205 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 $0.00057 $0.01205
Opus 5 $0.00028 $0.00602
Sonnet 5 $0.00011 $0.00241
Haiku 4.5 $0.00006 $0.00120

Measured yesterday against content hash f7129ca24521, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

diff-review 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.

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/diff-review/SKILL.md · 65 lines

How it starts

The opening of the file, as written. The whole thing — 65 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Diff Review

Find defects that would justify changing the candidate, with enough evidence for the author to reproduce and fix them.

Boundary

  • Review only by default. Do not edit code, resolve threads, commit, push, or approve a pull request unless the user separately requests that action.
  • Resolve the exact target and record base, head, working-tree state, and whether the evidence covers a dirty candidate, local commit, or remote pull-request head.
  • Preserve staged, unstaged, and untracked work. Use an isolated temporary worktree when broad validation would mutate or misrepresent the candidate.
  • Review against repository instructions, the issue or spec contract, and current source behavior. A green suite does not prove the intended behavior was implemented.
  • Report only actionable defects, material test gaps, or explicit requested nits. Do not manufacture findings to make the review look useful.

Workflow

  1. Resolve intent and target: Read the request, issue, spec, plan, and change description. Identify the exact comparison and proof already supplied.
  2. Inventory the delta: Inspect changed files, generated artifacts, dependency or schema changes, and nearby code needed to understand behavior. Do not review the diff in isolation when invariants live elsewhere.
  3. Read tests first: Determine what behavior the candidate claims, whether tests can fail for the defect class, and which requirements remain unproved.
  4. Trace intended versus implemented: Map permissions, user journeys, data rules, failure semantics, and operational promises to concrete code paths and tests.
  5. Review by risk: Examine correctness, data integrity, authorization, input boundaries, concurrency, resource lifecycle, error propagation, compatibility, migration, performance, observability, and rollback in proportion to the change. Challenge pass-through abstractions, hidden dependency construction, tests that bypass the public seam, and hypothetical flexibility with no second concrete use.
  6. Verify candidates: Reproduce each suspected defect with code tracing, a focused test, or a safe isolated temporary experiment. Quote the specific file and line that makes the finding real.
  7. Run proportional checks: Start with focused tests and static analysis; run the repository-owned full gate when cost and target coherence permit. Record exactly which candidate each result covers.
  8. Calibrate: Discard preferences and speculation. Rank remaining findings by user impact, exploitability, data loss, regression likelihood, and confidence.

Read the full file on GitHub · 65 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. yesterday First seen · 65 lines · 57 tokens per session scan A f7129ca24521

Subscribe to this mod's changes

diff-review is a skill published in the GitHub repository fmind/dotfiles (4 stars, last pushed 2d ago), licensed MIT. It adds 57 tokens to every session and 1,205 once invoked, about $0.0003 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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