---
title: MARKLESS_ATTRIBUTE_DUPLICATE
description: "Duplicate attribute on one element: a Markless compiler error."
sidebar: { hidden: true }
search: { keywords: ["ATTRIBUTE_DUPLICATE","attribute duplicate","markless error"] }
pagination: false
---

**Error** from the compiler, while it builds your `.tsrx` files.

## What happened

Markless prints the message, the reason, and a suggestion:

```text
MARKLESS_ATTRIBUTE_DUPLICATE: `<attributeName>` appears twice on <tag>. Only one can win, and render paths can disagree about which value is used.
Duplicate attributes ship invalid HTML and make the element depend on parser and update semantics instead of one authored value.
Keep one `<attributeName>` attribute on this element.
```

Words in angle brackets change from case to case.

## How to fix it

Start with the suggestion in the message above.

This page has no guide yet. [Help write it](/contributing/improve-these-docs).

## Where it comes from

`@markless/compiler` raises this code. Source:

- [packages/compiler/src/passes/semantic-graph/diagnostics.ts](https://github.com/compiled-run/markless/blob/main/packages/compiler/src/passes/semantic-graph/diagnostics.ts)

Read [how to read a Markless error](/tooling/diagnostics), or go back to [all error codes](/errors).