---
title: MARKLESS_REPEAT_KEY_IS_INDEX
description: "An @for loop is keyed by its index, so row state follows the position and not the item."
sidebar: { hidden: true }
search: { keywords: ["REPEAT_KEY_IS_INDEX","repeat key is index","markless error"] }
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---

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

## What happened

This loop uses `key i`. If the list reorders, any row state and event wiring stay with the slot number, not with the item.

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

```text
MARKLESS_REPEAT_KEY_IS_INDEX: key <indexName> identifies each row of <collectionSource> by its position, not by its data. If <collectionSource> reorders, inserts, or deletes, any row-local state, event wiring, and DOM reuse stay with the slot number.
The key is the identity root for a repeated graph scope; a positional key pins that scope to the slot, which is only correct when state genuinely belongs to the position.
Key by a stable field of the item when state belongs to the item, such as `@for (const <itemName> of <collectionSource>; key <itemName>.id)`. Keep `key <indexName>` when state should follow the slot.
https://markless.dev/errors/MARKLESS_REPEAT_KEY_IS_INDEX
```

Words in angle brackets change from case to case.

## How to fix it

If items can move, key by a stable field like `item.id`. If state belongs to the slot, keep `key i` and silence the warning with a reason.

```tsrx
<ul>
	// markless-allow MARKLESS_REPEAT_KEY_IS_INDEX: the list never reorders
	@for (const item of items; index i; key i) {
		<li>{item}</li>
	}
</ul>
```

## 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).