---
title: MARKLESS_REPEAT_KEY_DUPLICATE
description: "Two items in an @for list produced the same key."
sidebar: { hidden: true }
search: { keywords: ["REPEAT_KEY_DUPLICATE","repeat key duplicate","markless error"] }
pagination: false
---

**Error** from the runtime, while a page renders or runs.

## What happened

Two rows in the list have the same key, so Markless cannot tell them apart.

The error message reads:

```text
MARKLESS_REPEAT_KEY_DUPLICATE: Duplicate @for key <keyText> from <source>.
The key is each row identity across reorder, insert, delete, and resume; duplicate identities make row state and DOM ownership ambiguous.
https://markless.dev/errors/MARKLESS_REPEAT_KEY_DUPLICATE
```

Words in angle brackets change from case to case.

## How to fix it

Pick a key field that is unique across the whole list, like an id. Then check the data for repeated values.

## Where it comes from

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

- [packages/web/src/fns/direct.ts](https://github.com/compiled-run/markless/blob/main/packages/web/src/fns/direct.ts)
- [packages/web/src/fns/repeats.ts](https://github.com/compiled-run/markless/blob/main/packages/web/src/fns/repeats.ts)
- [packages/web/src/repeat-runtime.ts](https://github.com/compiled-run/markless/blob/main/packages/web/src/repeat-runtime.ts)
- [packages/web/src/resume-keyed-repeats.ts](https://github.com/compiled-run/markless/blob/main/packages/web/src/resume-keyed-repeats.ts)

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