Duplicate ID Checker
Paste your page HTML and find id attributes that collide or point nowhere — duplicates break labels, skip links and fragment URLs.
What this tool gives you
Check duplicate IDs
Paste your page HTML. Analysis runs locally in your browser — nothing is sent anywhere.
Duplicate ids break label[for], skip links, aria-labelledby and in-page anchors — getElementById returns the first match and ignores the rest.
What this checker looks for
One id, one element. Anything else is invalid HTML that assistive tech and browsers resolve differently.
Duplicate values
The same id on two nodes — labels and fragments hit the first only.
Empty id=""
Invalid, never matches a reference.
Dangling for / aria-*
label[for], aria-labelledby and aria-controls that point nowhere.
Broken skip links
href="#main" with no id="main" on the page.
Fragment URLs
In-page anchors that 404 inside the document.
0–100 score
Track uniqueness across templates and CMS partials.
How to keep IDs unique
One id, one element. Namespace anything a partial renders more than once.
Search for repeats
Grep the template for the colliding id and give each instance a unique suffix.
Match every reference
label[for], aria-labelledby, aria-controls and href="#…" must hit exactly one id.
Namespace CMS cards
If a card partial stamps id="title", prefix it with the item slug so repeats stay unique.
Why answer engines care about unique IDs
Unique ids are a cheap-to-parse signal that the document is well-formed and citation-ready.
| Signal | What engines infer | Why it helps |
|---|---|---|
| Unique ids | The document is valid HTML. | Parsers can resolve fragments and labels. |
| Working skip links | Keyboard paths were designed, not forgotten. | Engagement quality feeds crawl models. |
| Bound form labels | Every input has a named control. | Usable forms lower abandonment on AI-referred visits. |
| Stable fragments | In-page anchors do not 404 inside the document. | Citation-ready headings stay addressable. |
| No empty ids | Attributes were authored, not leftover from a template. | Citable, trustworthy pages get quoted more often. |
Related GEO pages
Unique ids pair with skip links and form labels so references actually resolve.
Duplicate ID FAQs
Why do duplicate IDs break a page?
HTML requires every id to be unique in the document. getElementById, label[for], aria-labelledby, skip links and fragment URLs all resolve the first match and ignore the rest. Two nodes sharing id="title" means one of them is unreachable to assistive tech and in-page anchors.
How do duplicate IDs usually get introduced?
CMS partials, repeated cards, and copied hero blocks stamp the same id onto every instance. A related pattern is generating ids from a heading slug without namespacing — two "Pricing" sections both become id="pricing".
What should skip links and labels point at?
Exactly one unique id. The skip link href="#main" needs <main id="main"> (or a wrapper with that id). A <label for="email"> needs <input id="email">. If the target is missing, the control or skip path silently does nothing.