"Does it run on my Mac?" — answered right on the Steam store.
A browser extension (Chromium, Manifest V3) by Sacha Gennari — s2c52
🔒 Your data never leaves your device. CrosTem has no servers, no accounts and no tracking — everything it stores lives in your browser, owned by you. Free & open source (GPL-3.0). Details ↓
Steam says "Windows only" for most of its catalog — but a huge share of those games run beautifully on a Mac through CrossOver, Parallels or Rosetta 2. The catch: finding out which ones means juggling three different community databases in separate tabs, every time you browse the store.
CrosTem folds all of that into Steam itself. Every game page gets a "Runs on Mac?" verdict — a conservative traffic light (🟢🟡🔴) computed from three community sources — plus star overlays on capsules across the whole store, and badges in search results and your wishlist. No accounts, no servers, no telemetry: the extension only fetches public compatibility pages and caches them in your browser.
CrosTem has no backend. There is no server of ours that receives, stores or even sees anything about you — no account to create, no sign-in, nothing to opt out of. Everything the extension knows (your settings, its cache of compatibility results, your match corrections) lives in your browser's storage, on your device, and belongs to you: inspect it, export it or wipe it from the options page whenever you like. And because CrosTem is free and open source, you don't have to take our word for any of this — anyone can read the code and verify every claim below.
- One single permission:
storage. Notabs, no browsing history, no cookies (manifest.json). - Everything stays on your device — the cache in
chrome.storage.local, your settings inchrome.storage.sync(which syncs through your browser profile, never through us). - Network requests go to exactly four public hosts — Steam (the page you're already on), CodeWeavers, AppleGamingWiki and AreWeAntiCheatYet's public dataset — enforced by a strict, unit-tested URL allowlist (src/lib/allowlist.ts), with external requests sent without credentials (
credentials: 'omit'). They only fetch public compatibility pages; nothing about you is ever sent anywhere. - No telemetry, no analytics, no error reporting, no tracking of any kind. Zero runtime dependencies, so no third-party library phones home either.
- Full policy: docs/privacy-policy.md (español).
| Source | What it contributes |
|---|---|
| CodeWeavers CrossOver database | Official CrossOver compatibility ratings ("Runs Great"…), stars, last-tested version and a per-version breakdown |
| AppleGamingWiki | Community status for CrossOver, Parallels, Rosetta 2 and native macOS builds |
| Are We Anti-Cheat Yet? | Anti-cheat support status — the #1 blocker for multiplayer games under CrossOver (Linux/Proton data, indicative) |
Steam's own same-origin appdetails API supplies the native-macOS flag and game metadata — native games are flagged directly, no external lookups needed.
The verdict engine (src/lib/verdict.ts) is a pure, fully-tested function with a deliberately conservative policy:
| Verdict | Meaning | When |
|---|---|---|
| 🟢 | Playable on Mac via CrossOver | CodeWeavers ≥ "Runs Well" (or ≥ 4★) or AppleGamingWiki ≥ playable — with no bad signal from the other source and no anti-cheat problem |
| 🟡 | Playable with caveats | Mixed or intermediate signals, or anti-cheat support merely Planned |
| 🔴 | Likely unplayable on Mac | Anti-cheat Denied or Broken (always forces red), or only negative compatibility signals |
| ⚪ | No compatibility data | Neither CodeWeavers nor AppleGamingWiki knows the game |
When the sources disagree, the widget says so explicitly ("Sources disagree — check both before buying") and shows each source's raw status so you can judge for yourself.
CrosTem renders on six surfaces, all individually toggleable:
- Game-page widget — a "Runs on Mac?" panel in the right column: verdict banner, collapsible per-source rows, the 3 latest CrossOver versions with stars (your branch highlighted), last-tested version, and direct links to each source. Skeleton shimmer while loading, retry on error.
- Store-wide capsule overlays — star ratings in the corner of game capsules everywhere (front page, sales, categories, "more like this"…), resolved lazily as each capsule scrolls into view.
?marks games with several possible matches;~marks approximate matches. - Search results & wishlist badges — compact rating badges next to each row's title, injected as rows appear (MutationObserver for Steam's AJAX search, generic
/app/link detection for the React wishlist SPA). - Toolbar popup — the active tab's verdict at a glance, manual game lookup, quick surface toggles and cache stats.
- Options page — toggle each surface and data source (changes apply live to open Steam tabs), set your CrossOver version, tune the cache TTL (1–30 days), and export/import your match corrections.
- Hover tooltip & onboarding — a mini-card with the verdict and per-source lines on badge hover, and a one-time onboarding page after install.
 |
 |
| Star overlays across the store | Badges in search results |
Plus:
- Native macOS games get a "Native on macOS" badge with 5 stars and an architecture tag — M Series (Apple Silicon) vs Intel (Rosetta 2 on M) — detected from AppleGamingWiki, Steam system requirements or release date (src/lib/arch.ts), without querying CodeWeavers at all.
- Ambiguous-match resolution — when a Steam name doesn't clearly map to a single CodeWeavers entry, the widget shows the candidates; pick once and CrosTem remembers it for that game everywhere ("Wrong match?" to change it). Corrections are kept per source and can be exported/imported.
Chrome Web Store: coming soon.
From source (Chrome, Brave, Edge — any Chromium browser):
git clone https://github.com/s2c52/CrosTem.git
cd CrosTem
npm install
npm run build # typecheck + vite build → dist/Then open chrome://extensions (or brave://extensions), enable Developer mode, click Load unpacked and select the generated dist/ folder.
The injected UI follows the language of the Steam page you're viewing — not the browser's — in all 30 languages Steam supports, detected from Steam's own page config (with ?l= and the Steam_Language cookie as fallbacks; src/lib/steam-lang.ts). Statuses quoted from the sources ("Runs Great", "playable"…) are intentionally left untranslated: they are citations, not UI copy.
flowchart LR
subgraph tab["Steam store tab (content scripts)"]
CS["app.ts · capsules.ts<br>search.ts · wishlist.ts"]
R["resolve.ts<br>verdict pipeline"]
C[("chrome.storage.local<br>TTL cache")]
CS --> R
R <--> C
end
subgraph sw["Service worker (background.ts)"]
Q["fetch queue<br>4 lanes · dedupe · per-source timeouts<br>retries + circuit breakers"]
A["URL allowlist"]
Q --> A
end
R -- messaging --> Q
A --> CW["codeweavers.com<br>(HTML, scraped)"]
A --> AGW["applegamingwiki.com<br>(MediaWiki cargo API)"]
A --> AC["AreWeAntiCheatYet<br>(games.json on GitHub)"]
R -- "same origin" --> SD["Steam appdetails API"]
- CodeWeavers has no public API, so the extension fetches their public pages (
/compatibility?name=…to search,/compatibility/crossover/<slug>for detail) and parses the HTML withDOMParser. All scraping lives in one file: src/lib/parser.ts. - The service worker proxies every external fetch — content scripts can't cross origins (CORS), the worker can via
host_permissions. It enforces a strict, unit-tested URL allowlist (src/lib/allowlist.ts): only the three sources' public endpoints, nothing else. Four concurrent lanes with in-flight deduplication, per-source timeouts (5–15 s underAbortController), retries with exponential backoff honoringRetry-After, and per-origin circuit breakers (src/lib/breaker.ts) so a slow or downed source fails fast instead of hanging badges — which then degrade to whatever the other sources report. - Everything is cached in
chrome.storage.local: results for 7 days (configurable 1–30), "no data" answers for 24 h, Steam details for 30 days, the anti-cheat dataset for 7 days — and your match choices permanently. Reads go stale-while-revalidate: a recently expired entry paints instantly while a background pass refreshes it and silently corrects the badge if anything changed. The cache maintains itself (in-memory L1, daily sweep, quota-safe writes, size-capped eviction). Settings live inchrome.storage.syncand apply live: toggling a surface mounts or unmounts it immediately on open Steam tabs, no reload. - Badges resolve ahead of time: a shared
IntersectionObserver(src/lib/auto.ts) triggers resolution about a viewport before a capsule scrolls into view, paints on the first source signal and refines when the rest arrive — while content scripts rescan only newly added page content (src/lib/scan.ts), so browsing the front page stays cheap. - No
innerHTMLanywhere — all UI is built withcreateElement/createElementNS, safe under strict CSP and Trusted Types. Accessible by design: star ratings carryrole="img"labels, verdicts are never conveyed by color alone, andprefers-reduced-motionis honored.
npm install
npm run dev # vite in watch mode (reloads the extension on save)
npm run build # typecheck + vite build → dist/
npm test # 241 unit tests (vitest + happy-dom, real HTML fixtures)
npm run lint # eslint
npm run e2e # Playwright against the real Steam store (headed Brave; E2E_HEADLESS=1 for CI)
npm run package # minified release build + zip for the Chrome Web StoreThe verification gate is scripts/verify.sh (typecheck + lint + tests + build); CI on GitHub Actions runs the same on every push (Node 22), audits dependencies and uploads dist/ as an artifact. The e2e suite also runs in CI on pull requests to development as a non-blocking job (headless Chromium; real Steam is too flaky for a gate) — the headed run before each release remains the authoritative check.
See CONTRIBUTING.md if you want to help, and SECURITY.md for reporting vulnerabilities.
All scraping lives in src/lib/parser.ts (selectors: #teTable-app for search; #appRating .os_Mac and #breakdown .breakdown-row for the detail page). The tests in tests/parser.test.ts will fail with new fixtures — the header comment explains how to recapture them.
The source code is licensed under the GNU General Public License v3.0 or later — see LICENSE. You are free to use, study, modify and redistribute it, provided derivative works remain under the same license.
Name and logo are not covered by that license. The "CrosTem" name and the extension icon are reserved by the author: forks and derivative distributions must use a different name and icon so users can tell them apart from the original extension.
The HTML files under tests/fixtures/ are captures of public pages from codeweavers.com, included solely as test fixtures; their content belongs to their respective owners and is not covered by the project license.
CrosTem displays data from these third-party sources, credited with thanks:
- CodeWeavers CrossOver compatibility database — CrossOver ratings and version breakdowns.
- AppleGamingWiki — macOS compatibility data (CrossOver, Parallels, Rosetta 2, native).
- Are We Anti-Cheat Yet? — anti-cheat status data.
- Steam appdetails API — platform flags and game metadata.
CrosTem is an independent project. It is not affiliated with, endorsed by, or sponsored by Valve Corporation (Steam), CodeWeavers (CrossOver), AppleGamingWiki, Are We Anti-Cheat Yet?, or Apple. All trademarks are the property of their respective owners. Compatibility ratings are community-reported data and carry no guarantee that a given game will work.