---
name: simplify
description: This skill should be used when the user asks to "simplify", "clean up the diff", "run simplify", "simplify the changes", "review changed code for cleanup", or explicitly invokes "/simplify". Reviews the changed code across reuse, simplification, efficiency, and altitude with parallel agents, then applies the fixes. Not for correctness bugs.
---
# Simplify
`/simplify → 4 cleanup agents in parallel → apply the fixes`
You are improving the quality of the changed code, not hunting for bugs. Review it for reuse, simplification, efficiency, and altitude issues, then fix what you find. Do not look for correctness bugs, that is what `/code-review` is for.
## Phase 0 — Gather the diff
Run `git diff @{upstream}...HEAD` (or `git diff main...HEAD` / `git diff HEAD~1` if there's no upstream) to get the unified diff under review. If there are uncommitted changes, or the range diff is empty, also run `git diff HEAD` and include the working-tree changes in scope, the review often runs before the commit. If a PR number, branch name, or file path was passed as an argument, review that target instead. Treat this diff as the review scope.
## Phase 1 — Review (4 cleanup agents in parallel)
Launch **4 independent review agents** via the Agent tool, all in a single message so they run concurrently. Pass each agent the diff and one of the four angles below. Each returns its findings with `file`, `line`, a one-line `summary`, and the concrete cost (what is duplicated, wasted, or harder to maintain).
### Reuse
Flag new code that re-implements something the codebase already has. Grep shared/utility modules and files adjacent to the change, and name the existing helper to call instead.
### Simplification
Flag unnecessary complexity the diff adds: redundant or derivable state, copy-paste with slight variation, deep nesting, dead code left behind. Name the simpler form that does the same job.
### Efficiency
Flag wasted work the diff introduces: redundant computation or repeated I/O, independent operations run sequentially, blocking work added to startup or hot paths. Also flag long-lived objects built from closures or captured environments, they keep the entire enclosing scope alive for the object's lifetime (a memory leak when that scope holds large values). Prefer a class/struct that copies only the fields it needs. Name the cheaper alternative.
### Altitude
Check that each change is implemented at the right depth, not as a fragile bandaid. Special cases layered on shared infrastructure are a sign the fix isn't deep enough, prefer generalizing the underlying mechanism over adding special cases.
## Phase 2 — Apply the fixes
Wait for all four agents to complete, dedup findings that point at the same line or mechanism, and fix each remaining one directly. Skip any finding whose fix would change intended behavior, require changes well outside the reviewed diff, or that you judge to be a false positive, note the skip rather than arguing with it. Finish with a brief summary of what was fixed and what was skipped (or confirm the code was already clean).