{"id":"ia.lang-attribute","name":"Language attribute","verify":{"command":"curl -sf https://{domain}/","rescan":"isagentready results {domain} --checkpoint ia.lang-attribute","expect":"The html element has a lang attribute"},"fix":{"steps":[{"action":"Set the lang attribute on the html element to the language of the page.","order":1,"language":"html","code_example":"<html lang=\"en\">"}],"summary":"Add a valid lang attribute to the html element.","skill":{"name":"content-semantics","anchor":"ia.lang-attribute"}},"category":"semantics","aggregate":null,"references":[{"title":"MDN lang attribute","kind":"guide","url":"https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/lang"},{"title":"W3C Declaring language in HTML","kind":"guide","url":"https://www.w3.org/International/questions/qa-html-language-declarations"}],"stage":"read","lifecycle":{"introduced":"2026-08-24","revised":[],"retired":null,"replaced_by":null},"methodology_version":"2026-10-22","evidence_tier":"standard","evidence_source":{"title":"MDN lang attribute","url":"https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/lang"},"why":"The lang attribute tells AI agents what language your content is in, enabling correct text processing, translation, and language-specific understanding.","profiles":["ai_search_visibility","browser_agent_usability"],"score_role":"core","legacy_id":"3.6","i18n":{"nl":{"name":"Taalattribuut","steps":["Zet het lang-attribuut op het html-element naar de taal van de pagina."],"why":"Het lang-attribuut vertelt AI-agents in welke taal je content is. Dat maakt correcte tekstverwerking, vertaling en taalbegrip mogelijk.","fix_summary":"Voeg een geldig lang-attribuut toe aan het html-element.","verify_expect":"Het html-element heeft een lang-attribuut"}},"ar_practice_ids":[],"strength":"MUST","ar_mapping":"none","evidence_type":"recommendation","detail_url":"https://isagentready.com/en/methodology/checkpoints/ia.lang-attribute","maturity":"essential","applicability":{"mode":"always","condition":null,"surfaces":["website"]}}