GitHub Contribution Chart Generator vs GitHub ReadMe Stats

This is a keyless JSON API (not an image-rendering service, despite the name) with a single route, `/api/v1/{username}`, that returns a GitHub user's daily/yearly contribution counts — confirmed by inspecting the project's own source tree, which contains only one API file (`src/pages/api/v1/[username].js`); the actual chart image is drawn client-side from that JSON by a separate canvas library. A live unauthenticated GET returned a 200 JSON payload with no `Access-Control-Allow-Origin` header at all, correcting cors from "yes" to "no" (the header only appears on Vercel's default 404 page, not on the real route). Free and open-source, self-hostable on Vercel.

GitHub Readme Stats generates SVG stat/language/pin cards for GitHub profile READMEs; its handler explicitly sets `Content-Type: image/svg+xml` and, per its own README, the shared public demo at `github-readme-stats.vercel.app/api` is "best-effort and can be unreliable due to rate limits and traffic spikes" (confirmed today: it returned a `DEPLOYMENT_PAUSED` 503) — the project itself is very much alive (58k+ GitHub stars, commits within the last week) and explicitly recommends self-hosting or a GitHub Actions workflow instead of relying on the shared instance. Neither the Vercel serverless handlers nor Vercel's platform add a CORS header by default, correcting cors from "yes" to "no". Free and open-source, self-hostable.