{"ok":true,"kind":"crawlcheck-rulebook","v":1,"generated_at":"2026-10-13T10:03:33.339Z","score_version":31,"schema":"https://crawlcheck.io/schemas/rulebook.json","counts":{"rules":86,"by_kind":{"scan":61,"answer_correlation":5,"capability_mismatch":6,"self_audit":12,"mcp_server":2},"by_family":{"site":16,"headers":4,"mostly_code":3,"machine_files":11,"nap":3,"robots":13,"delivery":8,"jsonld":3,"answers":5,"capabilities":6,"self_audit":12,"mcp":1,"watch":1},"revised":7,"scored":57},"scans_counted":3532,"severity_scale":[{"level":"info"},{"level":"low"},{"level":"medium"},{"level":"high"},{"level":"critical"}],"method":{"revisions":"A rule that changes what it reports gets a new revision; a record keeps the revision that decided it, and a replay uses that revision, never today's.","share":"Share of counted scans that carried the code at least once, the same numbers /data publishes. Self-scans and opted-out sites are never counted.","grade":"Each finding has a level from info to critical. Every graded finding lowers the score of its section; an open finding at medium or above also caps the letter grade, so fix those first."},"rules":[{"code":"IMAGE_FORMAT_MISMATCH","kind":"scan","family":{"id":"site","label":"Site, hosts and page"},"title":"Images are not the format their file names say","meaning":"An image's first bytes say one format while its file name says another (a .jpg that is a PNG, or an image address that returns an HTML page). It was fetched without asking for WebP or AVIF, so a CDN that converts on request is not counted. Browsers usually cope; image indexers and some clients trust the name, and an image address that returns a page is a broken image.","severity":{"level":"info"},"scored":true,"measured_on":"every scan","revision":{"current":1,"revised_at":null},"fix":{"advice":"Save each listed image under the extension of its real format (or re-export it in the format its name says), and fix image addresses that return a page.","effort":"content","endpoint":null},"share_of_scans":{"pct":0.2,"scans":6,"of_scans":3532,"basis":"share of counted scans that carried it; the same numbers /data publishes"},"links":{"self":"https://crawlcheck.io/rules#IMAGE_FORMAT_MISMATCH","api":"https://crawlcheck.io/api/rules?code=IMAGE_FORMAT_MISMATCH","glossary":[],"workflow":null,"lineage":"https://crawlcheck.io/docs/lineage-coverage","explain_template":"https://crawlcheck.io/api/explain?id={report_id}&code=IMAGE_FORMAT_MISMATCH"}}],"filter":{"code":"IMAGE_FORMAT_MISMATCH"}}