---
title: MARKLESS_REPEAT_KEY_REQUIRED
description: "An @for loop with state or events has no key."
sidebar: { hidden: true }
search: { keywords: ["REPEAT_KEY_REQUIRED","repeat key required","markless error"] }
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---

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

## What happened

The rows of this list have state or event handlers. Without a key, Markless cannot tell which row is which when the list changes.

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

```text
MARKLESS_REPEAT_KEY_REQUIRED: @for (const <itemName> of <collectionSource>) repeats reactive state without a key. When <collectionSource> changes, the rows of this list have no identity to update, reorder, or resume by.
A keyed loop item keeps its state, events, and DOM attached to the same logical item across reorder, insert, and delete; without a key there is no stable identity root.
Add a stable domain key such as `@for (const <itemName> of <collectionSource>; key <itemName>.id)`, or key by position with `index i; key i` when state should follow the slot.
https://markless.dev/errors/MARKLESS_REPEAT_KEY_REQUIRED
```

Words in angle brackets change from case to case.

## How to fix it

Add a key that stays the same for each item, like an id. If state belongs to the position in the list, key by the index instead.

```tsrx
@for (const item of items; key item.id) {
	<li>{item.name}</li>
}
```

## 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).