# Lang / charset
_Source: https://seomatrix.ai/tools/lang-charset/_
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## What it does
This tool inspects the four head essentials of any HTML page you point it at by URL: the html lang attribute, the meta charset declaration, the viewport meta tag, and the doctype. These are the signals browsers, search crawlers, and AI answer engines rely on to decode your text correctly, identify its language, and render the page on mobile. A missing charset garbles your copy, a missing or wrong lang misfiles the page by language, and both quietly undermine how reliably an engine can read and cite you.
## What it checks
- **html lang attribute** — The lang value on the tag declares the page's primary language as a BCP 47 code, which screen readers, browsers, and AI engines use to interpret the text and attribute it to the right language.
- **meta charset** — A declaration tells the browser how to decode the raw bytes; without it, accented and non-ASCII characters render as mojibake (garbled symbols).
- **charset position** — The charset declaration must appear within the first 1024 bytes of the document, or the browser may begin parsing under the wrong encoding before it ever reaches the tag.
- **viewport meta tag** — The tag controls how the page scales on phones; missing it makes the page render at desktop width and fail mobile-friendliness checks used in mobile-first indexing.
- **doctype declaration** — The line at the top of the document triggers standards-mode rendering; without it browsers fall back to quirks mode and lay out the page inconsistently.
- **valid language code** — The lang value must be a real BCP 47 tag such as en, es, ru, or pt-BR rather than empty or invented, or browsers and assistive technologies mishandle the page's declared language. (hreflang uses its own language codes in link tags and does not depend on this attribute.)
## How to use it
1. Paste your page URL and run the check.
2. Review the flagged head elements — missing or malformed lang, charset, viewport, or doctype.
3. Fix them in your page template or CMS and re-run the check to confirm.
## FAQ
### Does a missing charset really cause problems if my page looks fine?
Yes — a page can look fine in your browser because it guessed the encoding, but other browsers, crawlers, and AI engines may decode it differently and produce garbled text. Declaring removes the guesswork.
### What should the html lang attribute be set to?
Set it to the BCP 47 code of the page's main language — en for English, es for Spanish, ru for Russian, or a regional variant like pt-BR. It goes on the opening tag: .
### Is the viewport meta tag required for SEO?
It is effectively required for mobile-friendliness, which Google uses for mobile-first indexing. Without , mobile pages render zoomed out and fail the mobile usability check.
### Does this tool fix the problems it finds?
No — it inspects the live HTML of the URL you enter and reports which head elements are missing or malformed. You apply the fixes in your template or CMS, then re-run the check to confirm.