Validators
HTML Validator
Paste HTML on the left, hit Run, copy a pass/fail with a reason, not a shrug. No Node, no pip, no Docker for a five-minute job. That is the html validator.
Drop a file on the left. Drafts stay in this browser. Shortcut: Ctrl or Cmd + Enter to run.
How this html validator works
- Paste or drop a .html file into the input on the left.
- Flip options if you see them (comments, indent, case). Defaults are the safe ones.
- Hit Run, or Ctrl / Cmd + Enter. Leave “Process on server” off unless you mean it.
- Read the status line, then copy, download, or jump to a related tool.
What this html validator is for
The file is already in front of you. You need to validate it without opening a whole IDE profile. Paste, run, copy. Typical timing: before you save a config, publish an API sample, or paste a token into docs.
You walk away with a pass/fail with a reason, not a shrug.
What it will not pretend to be
This is not a full W3C HTML auditor or a cryptographic verifier unless the page says so. Whitespace is not always free in HTML. Space between inline tags can become a visible gap, and content inside <pre>, <textarea>, and <script> should not be smashed the same way as a <div>.
By default nothing leaves the tab. Tick “Process on server” only if you want to compare results or use gzip numbers that match the server library.
A practical way to use it
Drop a .html file onto the input or paste. Flip options if they are there. Run. Read the status line. Copy or download. Drafts stay on this device so a refresh does not punish you.
When you are done, hop a related tool instead of starting over: minify and beautify toss the file back and forth, format and validate often share a parser, convert wants valid input first.
The small print that saves a round-trip
Whitespace is not always free in HTML. Space between inline tags can become a visible gap, and content inside <pre>, <textarea>, and <script> should not be smashed the same way as a <div>.
You searched “html validator online.” You got an editor, not a login wall. That is the deal.
Frequently asked questions
What does “valid HTML” mean here?
A pass means the checker could parse the HTML you pasted. A fail should tell you why — a missing brace, a trailing comma, a tag that never closed. Example of a happy JSON object: {"ok":true}. Example of a trap: {ok:true,} — that trailing comma is JavaScript, not JSON.
Should I validate HTML before I go live, or while I edit?
Edit in a readable shape. validating belongs to the moment the file has to be understood (beautify/format/validate) or the moment it leaves your hands (minify/encode). Mixing those moods is how minified HTML becomes your only source of truth — a sad place to live.
Can validating HTML break what I already put live?
Whitespace is not always free in HTML. Space between inline tags can become a visible gap, and content inside <pre>, <textarea>, and <script> should not be smashed the same way as a <div>. Glance at the output once. A 20-second read beats a 20-minute “why did production go weird” thread.
Got a simple before-and-after for html validator?
Sure. Before: <h1 class="hero">\n Hello\n</h1> After: <h1 class="hero">Hello</h1>. That is the whole mood of the tool — same job, different clothing. If your real file is huge, try a representative slice first so you can see the rule, not a wall of text.
What about comments, strings, and data that look like code?
Strings are data. 'a + b' is not math. Comments are notes — minify may drop them, beautify should keep them if the engine sees them. HTML has its own trap: Whitespace is not always free in HTML. Space between inline tags can become a visible gap, and content inside <pre>, <textarea>, and <script> should not be smashed the same way as a <div>.
Any fun HTML fact worth remembering?
Fun fact: HTML collapses most extra spaces into one, but a single space between <a>Docs</a> <a>API</a> is still a real gap on the page. Minify that space and the links kiss.
Do I still need a bundler, Prettier, or a schema tool?
For an app in git: yes — keep the project formatter and the bundler. This html validator is for the five-minute paste: a log line, a vendor dump, an email template, an API body. Different altitude, same mountain.
When should I not use a html validator?
Skip it when the file is a binary, when you need a full language compiler, or when a single sample cannot represent the format (Excel workbooks, YAML with anchors, HTML that is really a React tree). Also skip minify as your only copy of source. Keep a readable original.