RSS/Atom Feed Validator API - Validate RSS, Atom and JSON Feed, graded as JSON

Hi everyone, this is RSS/Atom Feed Validator API. Give it a feed URL, or a website that advertises its feed, and it returns a JSON report: the detected format, XML well-formedness checks (mismatched tags, bare ampersands, undefined entities, with line numbers), required and recommended elements, RFC 822 and RFC 3339 dates, duplicate guid/id values, enclosure attributes and basic podcast fields. Issue codes are stable snake_case strings with a severity of error, warning or info, plus an overall grade (A+ to F) and a score out of 100. Formats: RSS 2.0 (and older 0.9x), Atom 1.0 (RFC 4287), RSS 1.0 (light checks) and JSON Feed 1 / 1.1. Two endpoints: - GET /v1/check?url= reads the URL (up to 5 redirects, first 1 MB). If it is an HTML page it follows the first feed and lists up to 4 others under discoveredFrom. Cached for 6 hours per URL; fresh=1 bypasses the cache. - POST /v1/validate checks feed text you send in (XML or JSON Feed, up to 1 MB), offline, with no outbound request. Limits: the rule set and the XML parser are our own, so results can differ from other validators and do not guarantee acceptance by any podcast directory or feed reader. Feeds over 1 MB return grade unchecked, and a URL that is not a feed returns not_a_feed; neither is a pass. One error scores 75 (grade C), so gate on summary.errors rather than on the grade alone. Private-network targets are rejected. Not affiliated with the W3C or any feed reader. Where to find it: RapidAPI (public, https://rapidapi.com/tossneon0/a...), API.Market and APIHub. Product site: https://feed-validator.glowhalo.org Feedback on the checks and the scoring is welcome.