HTML Validator

Run bundled html-validate rules against the supplied HTML source without executing it. Checks document structure, attributes and selected accessibility rules.

Free to useNo sign-upRuns in your browser

Enter your details

Enter the inputs, then select Validate HTML.

Your result

Enter your details

Result will appear here

How HTML Validator works

Run bundled html-validate rules against the supplied HTML source without executing it.

The tool processes the supplied input with browser APIs and bundled local libraries.

Concept diagram for HTML Validator, showing html document input and the supported output. — Concept diagram; the three operation images are actual browser captures.

How to validate HTML

Supply supported input and review the result.

Enter the source details

Replace the example with your HTML document.

Validate HTML

HTML Validator: input and settings in the implemented browser tool — Actual local browser view. Open the image to read it at full size.

Review the conversion settings

Check the supported input and conversion limits below.

Validate HTML

HTML Validator: tool result in the implemented browser tool — Actual local browser view. Open the image to read it at full size.

Review the diagnostics

Read reported locations and rules, then revise the source.

Validate HTML

HTML Validator: review the details in the implemented browser tool — Actual local browser view. Open the image to read it at full size.

When to use HTML Validator

Find structural markup issues

Diagnostics show line and column positions in the supplied source. Use those locations to revise the original document.

Validate HTML

Developer input and configuration represented by document cards. — Prepare the input. Concept illustration.

Review selected accessibility rules

Configured rules can report markup issues such as missing attributes. They do not replace keyboard, screen-reader or visual testing.

Validate HTML

A developer example flowing from input to reviewed output. — Inspect an example. Concept illustration.

Check source without running it

The validator parses text without executing scripts. CSS, JavaScript and actual layout need separate checks.

Validate HTML

Developer output handed to the next stage of a workflow. — Use the result in your workflow. Concept illustration.

What the output contains

Review the format and conversion policy.

HTML markup diagnostics with line and column locations. Checks document structure, attributes and selected accessibility rules. It is not the W3C service and does not validate CSS, JavaScript, actual browser rendering or full accessibility compliance.

Keep the original while checking the saved output. The result reflects the input and settings you supplied.

Validate HTML Validate HTML

A developer result reviewed alongside its source. — Review the returned output. Concept illustration.

Supported input and limits

Check these conditions before converting.

Checks document structure, attributes and selected accessibility rules. It is not the W3C service and does not validate CSS, JavaScript, actual browser rendering or full accessibility compliance.

The page does not keep inputs or results after leaving. Keep the source and save the output you need.

Validate HTML Validate HTML

Input format and assumptions reviewed for a developer task. — Check format and assumptions. Concept illustration.

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Validate HTML with your input

Review the supported output and save your result.

Validate HTML

HTML Validator: common questions

Answers about using HTML Validator and understanding its results.

What output can I save?

Save HTML markup diagnostics with line and column locations. Checks document structure, attributes and selected accessibility rules. It is not the W3C service and does not validate CSS, JavaScript, actual browser rendering or full accessibility compliance.

Does the page upload my input?

No. Processing uses browser APIs and bundled local libraries. The selected file or entered source is not sent to a conversion server. Save the result before leaving.