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/html

well-formed HTML — tags nest correctly, declared charset matches body bytes, doctype matches markup version, no tag left open

chaos chaos.catastrophic.io

GET /html

Returns HTML documents with deliberate structural flaws. Useful for testing browser parsers, scraper robustness, and ML preprocessing pipelines that ingest HTML. Default mode produces visible misnesting on a bare GET; other modes target charset, doctype, or unterminated-tag handling.

modes: mismatched-tags meta-charset-conflict doctype-mismatch script-without-end

full chaos docs →

control not.catastrophic.io

GET /html

well-formed HTML — tags nest correctly, declared charset matches body bytes, doctype matches markup version, no tag left open

full control docs →

Build against not.catastrophic.io/html, then flip the hostname to chaos.catastrophic.io to exercise the chaos.