Use an HTML validator or checker to assess a document against defined markup rules; use an editor-integrated linter when you want diagnostics as you write. Those jobs overlap, so choose by the checks and workflow a tool actually provides—not its label. Neither a clean result nor valid markup by itself proves that a page is accessible or fully conformant.
What is the difference between an HTML linter and an HTML validator?
An HTML validator checks a document against defined syntax or specification rules and reports discrepancies. A linter is a broader term for a development tool that surfaces diagnostics during coding, often in an editor or build workflow. In practice, the categories are not mutually exclusive: the W3C Markup Validation Service describes its validator as “sort of like lint for C.”
That overlap means “validator” does not always mean syntax-only, and “linter” does not always mean style-only. Some checkers also flag issues that may point to accessibility, usability, interoperability, security, maintainability, performance, parsing, or scripting problems. Treat those reports as warnings about potential problems, not a complete assessment of those qualities.
What does a passing validation result establish?
It establishes that the document passed the particular checks the tool ran. W3C distinguishes validity from conformance: meeting a formal grammar is only part of conformance, because some requirements cannot be expressed in that grammar. Validation therefore is not a certificate that a page meets every requirement of a specification.
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The Nu Html Checker explicitly cautions that it is a checker, not a pass/fail certification mechanism. W3C’s WCAG technique likewise presents validation as an automated check against a specification, not sufficient proof that every accessibility requirement is met. Use validation to find markup problems, then assess accessibility and any other relevant requirements separately.
Which tool should you use?
| Your need | Start with | Reason |
|---|---|---|
| Check a page or document against HTML rules | Nu Html Checker | It is presented as an HTML checker and validator; the W3C tools directory lists it. |
| See feedback while editing in Visual Studio Code | HTMLHint | Its official site advertises real-time HTML feedback through a VS Code extension. |
| Automate checks from a command line or service workflow | Nu Html Checker | The project describes standalone command-line and HTTP service modes in its repository. |
| Determine whether a page is accessible or fully conformant | Validation plus separate assessment of the relevant requirements | Validation alone does not establish full conformance. |
How to compare tools before adding one
- Checks: Read what rules and issue types the tool reports; do not infer scope from “linter” or “validator.”
- Feedback location: Decide whether you need diagnostics in an editor, a command-line run, or an HTTP service.
- Configuration: Check whether you can tune the rules to fit your project and workflow.
- Meaning of a pass: Establish what the tool checked and what remains outside its scope.
The Nu Html Checker documentation notes that checks are actively added and results for the same document are not guaranteed to remain identical over time. For a time-sensitive or automated workflow, review the checker’s current behavior and avoid treating its output as a permanent certification.
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