---
title: MARKLESS_REPEAT_KEY_UNSTABLE
description: "@for key must identify the item stably: a Markless compiler error."
sidebar: { hidden: true }
search: { keywords: ["REPEAT_KEY_UNSTABLE","repeat key unstable","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_REPEAT_KEY_UNSTABLE: key <keySource> does not derive identity from <itemName> or an explicit index alias. Row state, event wiring, and DOM reuse follow the key, so rows of <collectionSource> could not be matched with themselves reliably.
The key is the stable identity root for a repeated graph scope across reorder, insert, delete, and resume; a value that is not derived from the item or its position cannot identify anything.
Key by a stable field of <itemName>, such as `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_UNSTABLE
```

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).