Language and encoding — agent readiness

Why an agent cares

An undeclared or late charset makes an agent guess, and a wrong guess corrupts every non-ASCII character it reads. A malformed lang tag is a smaller problem but the same kind: the declaration is there and cannot be used.

Adoption

Web baseline. Standard equipment on the web. Its absence is the exception rather than its presence.

Direction of travel: ► flat, as at 2026-07-28.

BCP 47 and UTF-8 are near-universal; UTF-8 is on roughly 98% of pages (W3Techs).

What we check

Absence is never a finding. Every check below runs only when this technology is detected, so a site that has not adopted this is not assessed on it and appears in no report. 5 of these 5 can fail it. In Lumar these appear on each page's own row.

Check	Severity	Raises	On whose authority
Charset Missing	high	conformance, usability	specification: WHATWG HTML — the lang attribute
Supporting documents: WHATWG HTML — the lang attribute Required by WHATWG HTML — the lang attribute. Bad: neither the HTTP Content-Type header nor an in-page <meta charset> declares the encoding, so agents may decode the bytes wrongly and garble the text. Fix: declare UTF-8, ideally in the header: Content-Type: text/html; charset=utf-8.
Lang Missing	medium	usability	specification: WHATWG HTML — the lang attribute
Supporting documents: WHATWG HTML — the lang attribute Related guidance in WHATWG HTML — the lang attribute. Bad: <html> has no lang attribute, so agents and translators must guess the page language and can guess wrong. Fix: declare it on the root element, e.g. <html lang="en">.
Lang Invalid BCP 47	medium	usability	Lumar readiness bar, beyond BCP 47 — Tags for Identifying Languages
Supporting documents: BCP 47 — Tags for Identifying Languages Lumar readiness bar: no specification requires this. Bad: the lang value isn't a usable BCP 47 tag (a name like "english", or an underscore form like "en_US"), so consumers ignore it. Fix: use a valid tag such as "en" or "en-US" (hyphen, not underscore).
Charset Non-UTF-8	medium	conformance, usability	specification: WHATWG HTML — the lang attribute
Supporting documents: WHATWG HTML — the lang attribute Required by WHATWG HTML — the lang attribute. Bad: the page's effective encoding isn't UTF-8, which HTML requires of every document and which modern agents assume, so characters can arrive corrupted in anything that reads it. Fix: re-save the page as UTF-8 and declare it, either as Content-Type: text/html; charset=utf-8 or as <meta charset="utf-8"> — the Charset Declaration Source column says which one to change.
Charset Late	medium	conformance, usability	specification: WHATWG HTML — the lang attribute
Supporting documents: WHATWG HTML — the lang attribute Required by WHATWG HTML — the lang attribute. Bad: the charset <meta> ends after the first 1024 bytes of the document, past where parsers pre-scan, so it may be ignored. Fix: put <meta charset="utf-8"> first in <head>, or declare the charset in the Content-Type header.

Examples

Both run through the same checks as a live scan: the first passes, the second is flagged.

correcthtml

<html lang="en">

    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>How agent-readiness works — Example</title>
    <link rel="canonical" href="https://example.com/content/correct.html" />

present but wronghtml

<html lang="english">
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>How agent-readiness works — Example</title>

    <meta name="description" content="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" />
    <meta charset="ISO-8859-1" />

Specifications

Document	Revision	Kind
BCP 47 — Tags for Identifying Languages	Current best practice	specification
WHATWG HTML — the lang attribute	Living Standard	specification
WHATWG Encoding Standard	Living Standard	specification
WHATWG HTML — meta charset (within the first 1024 bytes)	Living Standard	specification

Last re-read against the published documents: 2026-10-05.