---
name: simplify
description: Daily-driver review of in-flight changes (or specified files) for reuse, simplification, efficiency, and high-confidence bugs. Flags code that duplicates existing helpers, overengineering, dead code, hot-path bloat, premature abstraction, real correctness issues, and unnecessary comments or tests. Default mode diffs the working tree and staged changes against the main branch. Pass paths (`/simplify src/foo.rs`) to review file state instead. Use as the fast pre-PR review pass. For a deeper whole-tree retrospective, use /audit.
---

# /simplify

Simplification review of work-in-progress. Default runs against the current diff. Explicit paths switch to file-state review.

## Invocation

```
/simplify                          # diff working tree + staged vs main/master
/simplify --staged                 # only staged changes
/simplify --branch develop         # diff against a different base
/simplify src/foo.rs               # review one file as-is (ignores diff)
/simplify src/foo/ src/bar.rs      # review multiple paths as-is
```

Paths win: if any are given, ignore the diff and review file state.

## Gathering context

Diff mode:

1. Resolve the base branch. Try `git symbolic-ref refs/remotes/origin/HEAD`, then `main`, then `master`. Ask the user if neither exists.
2. With `--branch <name>`, use that base instead.
3. With `--staged`, use `git diff --cached <base>`. Otherwise include working tree (`git diff <base>...HEAD` plus uncommitted).
4. Read each touched file fully, not just the hunks. Context outside the diff is needed to spot duplication and existing helpers.

File mode: read each passed path (recurse into directories, skip generated and vendored trees).

Always: read `CLAUDE.md` (root and any in touched dirs) and `TODO.md` / `BACKLOG.md` if present. Honor local conventions and do not re-raise deferred items.

## What to flag

### Reuse (look here first)

- New helpers or inline logic that duplicates an existing utility in this codebase. Scan the file's directory and shared locations (`utils/`, `lib/`, `helpers/`, modules adjacent to the changed ones) before concluding nothing exists.
- Reinvented standard library or framework primitives (manual path joining, ad-hoc env var parsing, custom type guards, hand-rolled string manipulation, bespoke deep-equals, etc.) where the language or an in-repo helper already covers it.
- Inconsistent import paths for the same thing (some sites use a top-level re-export, others reach into deep paths). Pick the path the rest of the codebase uses.
- For each duplication finding: name the existing helper with `file:line` so the fix is concrete, not abstract.

### Overengineering

- New helpers, traits, generics, or indirection introduced for one caller. Inline.
- Flags, parameters, or fields with only one realistic value or use site.
- Layers added speculatively without a current second caller.

### Dead code in the same change

- Functions added but uncalled elsewhere in the diff.
- Branches that cannot be reached given the rest of the change.
- New types, fields, or variants that nothing constructs.

### Bugs (high-confidence only)

Flag only when the issue is clearly wrong on inspection. "This might fail under some inputs" is not a finding.

- Logic errors: off-by-one, wrong condition in `if`, inverted comparison, incorrect loop termination, swapped arguments.
- Missing bounds checks where the input is not otherwise validated.
- Type confusion that compiles but is wrong (mixing units, conflating IDs, using one enum where another was meant, comparing values of different shapes).
- Null or undefined access in JS/TS where the type allowed it but the path is reachable.
- Async lifetime mistakes: missing `await`, awaiting the wrong promise, dropping a future, fire-and-forget where the result was meant to be used.
- Rust borrow or lifetime patterns that compile but violate the intended invariant (lifetimes too permissive, `Send`/`Sync` boundaries crossed by accident).
- Resource leaks: opened but never closed, listeners attached but never removed on the failure path.

### Efficiency

Focus on hot paths (per-render, per-request, per-frame, per-record) and on patterns that get worse with scale.

- Redundant work: duplicate computations, repeated file reads, redundant API or network calls, N-plus-one query patterns (one query per item where one batch query would do).
- Independent operations run sequentially that could run in parallel.
- New blocking work added to startup or per-render/per-request paths that did not have it before.
- State updates inside polling loops or event handlers that fire even when nothing changed. Add change-detection so downstream consumers are not woken for no-ops. If a setter takes an updater callback, verify same-value returns are honored so callers' own no-op guards are not silently defeated.
- Pre-checking a file or resource for existence before operating on it. This creates a race where the resource can change between the check and the use. Operate directly and handle the error from the operation instead.
- Unbounded data structures, missing cleanup, leaked event listeners or timers.
- Operations broader than they need to be (reading entire files when only a portion is needed, loading all rows when filtering for one, scanning a whole collection to find a single item where an index already exists).

### Premature flexibility

- `Option<T>` where the value is always `Some`.
- Trait bounds or generic parameters wider than the actual use.
- Enum variants for cases that do not yet exist.
- `impl Trait` where the concrete type would read just as clearly.

### Comments to delete

- Narration of what the code does (`// increments counter`).
- Section dividers (`// ---`, `// === FOO ===`).
- References to the task or commit that prompted the change ("added for X", "used by Y", "fixes #123").
- Stale docs where the code has moved past them.

### Tests not pulling weight

- Tests that assert the language or framework's behavior rather than the new logic.
- Tests duplicated across files with no extra coverage.
- Fixtures wrapping a one-liner for a single test.
- Mocked tests where an integration test already covers the same path.

### Scope creep

- Unrelated formatting changes mixed in with functional changes.
- Drive-by refactors in files outside the stated goal.
- "While I'm here" cleanup that belongs in a separate commit.

### Style-rule violations (from the user's global CLAUDE.md)

Flag these whenever they appear in the diff or files, no preamble required:

- Em-dashes, en-dashes, `--` as em-dash substitutes, and semicolons in prose (comments, docs, commit messages, PR descriptions).
- Programming-culture acronyms (YAGNI, DRY, KISS, SOLID, TDD, BDD, DDD, MVP, NBO, TOCTOU) in any prose. Replace with what they actually mean.
- Section divider comments.
- Milestone references in code docs ("for M2", "added in M1").
- `Co-Authored-By: Claude` trailers in commit messages.

Fold in any project-local `CLAUDE.md` conventions on top of these.

## What NOT to flag

- Low-confidence speculation. "This might break under some inputs" is not a bug finding. "This could be faster in theory" is not an efficiency finding. If you cannot point at a concrete failure mode or a concrete cost, leave it out.
- Issues a linter or formatter already catches.
- Missing tests or coverage gaps (separate concern, not a simplification).
- "You could rewrite this with library X" or other broad architectural rewrites.
- Items already in `TODO.md` / `BACKLOG.md`.
- Performance theatre: micro-optimizations outside hot paths.

## Reporting

Single pass, all findings together. No tiered ceremony.

```
## Simplification pass

<N> findings on <scope>.

1. path/to/file.rs:42-58 - <issue, one line>.
   Fix: <one-line change>.
2. path/to/file.rs:88 - <issue>.
   Fix: <one-line change>.

Apply all? "Go ahead", or tell me which to skip.
```

If a finding touches public API or changes behavior beyond cleanup, surface it as **Needs discussion** with two options rather than dropping it in the auto-apply list.

If nothing is worth flagging, say "Nothing flagged" in one line and stop. Do not pad.

## Applying

After approval:

1. Apply only approved findings.
2. Diff mode: fold edits into the working tree. Do not commit unless the user asks, since they are mid-PR.
3. File mode (no in-flight diff): default to one commit per theme using Conventional Commits.
4. Run the project gate (`scripts/prepare.sh`, `pnpm check`, `cargo test`, equivalent) when applying multiple substantive changes.

## Do not

- Rewrite history. The user is preparing a PR. Do not squash or amend existing commits.
- Auto-apply changes to public API surface. Lift those into **Needs discussion**.
- Touch files outside the diff (diff mode) or outside the passed paths (file mode).
- Reference the simplify pass in commit messages ("from /simplify", "simplification cleanup"). Describe the change, not how it surfaced.
- Surface a "bug" or "perf" finding you are not confident about. The signal value of this skill comes from the user trusting flagged bugs are real. False alarms erode that fast.
- Pad. If the diff is clean, "Nothing flagged" is the right answer.
