Borrowing it
Nothing to install: this file belongs to shift-editor/shift. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/shift-editor/shift/main/.agents/skills/perf/SKILL.mdgit clone --depth 1 https://github.com/shift-editor/shiftWrote 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.
[](https://agentmods.dev/skills/shift-editor/shift/perf)<a href="https://agentmods.dev/skills/shift-editor/shift/perf"><img src="https://agentmods.dev/badge/skills/shift-editor/shift/perf/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/shift-editor/shift/perf"><img src="https://agentmods.dev/badge/skills/shift-editor/shift/perf.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00089 | $0.04250 |
| Opus 5.5 | $0.00036 | $0.01700 |
| Sonnet 5.5 | $0.00018 | $0.00850 |
| Haiku 4.5 | $0.00009 | $0.00425 |
Grade A, and why
perf 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.
How it starts
The opening of the file, as written. The whole thing — 132 lines — stays where its author put it; the contents beside it link to each section on GitHub.
/perf — Measuring and fixing slowness in Shift
Measure the build users run, find what started the work, fix that, and measure again with the same command. A guess that "this looks expensive" has been wrong more often than right here; a number with a cause attached has not.
1. Measure a packaged production build
Never draw conclusions from pnpm dev. React's development build adds jsxDEV, prop validation, and render logging that made up about half of every dev profile and pointed at the wrong code.
pnpm profile:build # native bridge (release) + renderer minified like a release, with source maps and component names (~1 min warm)
pnpm profile:desktop --font <path> [--glyph A] [--scenario scrub] [--axis Weight] [--seconds 8] [--cpu out.cpuprofile]
profile:desktop launches the packaged app with a throwaway profile, opens the font and glyph, drives the scenario with real pointer input, and prints:
- Frame times (p50/p90/p99, frames over 33 ms) — the number the user feels.
- React renders per commit, and for each re-rendered subtree the component and the hook slot or context that started it. This is what tells you what to fix.
- A source-mapped CPU profile — busy time, top self time, top inclusive time in Shift code. Open the saved
.cpuprofilein Chrome DevTools for flame charts.
Notes:
- The packaged app is in
apps/desktop/out/<platform>-<arch>/(linux-unpacked/shifton Linux). Olderout/Shift-*directories are stale Electron Forge output; ignore them. - Packaged builds disable Node's inspector fuse, so Playwright's
_electron.launchcannot attach. The script uses Chromium's--remote-debugging-portandconnectOverCDPinstead. - On a remote or headless Linux session the app needs the desktop's environment (
DISPLAY/WAYLAND_DISPLAY,XDG_RUNTIME_DIR,DBUS_SESSION_BUS_ADDRESS), and must not inherit a NixLD_LIBRARY_PATH. - Linux needs Chromium's
Vulkanfeature for WebGPU; without a GPU adapter the glyph grid falls back and the numbers mean nothing. - Add a scenario to
scripts/profile-desktop.mjsrather than writing a one-off script, so the next person can rerun your measurement.
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.
- 3d ago Changed · +9 lines c509f2809a43
- 7d ago Changed · +53 lines · +25 tokens per session 4ccc6aa74e9f
- 11d ago Changed · +1 lines 68e606021dd4
- 20d ago First seen · 69 lines · 64 tokens per session scan A dae8b50de66e
perf is a skill published in the GitHub repository shift-editor/shift (379 stars, last pushed today), licensed Apache-2.0. It adds 89 tokens to every session and 4,250 once invoked, about $0.0004 per session on Opus 5.5. 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 2026-10-09.
Other skills, from other repositories
systematic-debugging
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performance-profiling
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lint-and-validate
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verify-changes
Prove code works by running it, not just checking it exists. Verification through execution rather than inspection. Use after writing or modifying code to ensure it actually functions correctly.
migrate-oxlint
Guide for migrating a project from ESLint to Oxlint. Use when asked to migrate, convert, or switch a JavaScript/TypeScript project's linter from ESLint to Oxlint.
moli-webfetch
Fetch, inspect, crawl, and capture live, JavaScript-rendered websites with Moli. Use when Codex needs current web content, web research, fact lookup, link following, a bounded crawl, client-rendered or response-gated content, network diagnostics, or a standalone HTML, Markdown, JSON, semantic-tree, viewport or…