{"rule_id":"AB-046","category":"infrastructure","icon":"🚫","title":"Structured 404 Errors","short_description":"Your site returns structured JSON for 404 errors instead of plain HTML.","user_value":"When agents hit a missing page, a structured error tells them what went wrong. An HTML 404 page is useless to machines.","wrong_example":"404 returns an HTML page. Agents can't parse the error.","right_example":"404 returns structured JSON with error details agents can understand.","effort_hint":"quick","estimated_cost":"$0","severity":"medium","pillar":"verifiability","version":"1.0.0","counted_in_score":true,"check":{"type":"http_probe","sources":["content_negotiation"],"target":"/nonexistent"},"fix":{"eligible":true,"type":"deterministic","note":"Return JSON error body for 404 responses"},"checklist_anchor":"#AB-046","checklist_url":"/agent-readiness-checklist#AB-046","html_url":"/rules/AB-046","json_url":"/rules/AB-046.json","related_rules":[{"rule_id":"AB-045","title":"Cache Headers","category":"infrastructure"},{"rule_id":"AB-047","title":"Rate Limit Headers","category":"infrastructure"},{"rule_id":"AB-073","title":"HTTPS Redirect Enforced","category":"infrastructure"},{"rule_id":"AB-098","title":"Content-Security-Policy header","category":"infrastructure"},{"rule_id":"AB-099","title":"Referrer-Policy header","category":"infrastructure"}]}