---
title: 'CHR0067: A node needs exactly one key'
editUrl: https://github.com/Cratis/Chronicle/edit/main/Documentation/code-analysis/CHR0067.mdx
description: CHR0067 reports a node without exactly one key, or an edge with more than one key.
lastUpdated: 2026-11-05T00:00:00.000Z
---


## Rule description

A node is identified by exactly one property marked with `[Key]`. An edge is identified by its type, its source and its target. An edge can additionally have one property marked with `[Key]`, which identifies it among edges of the same type between the same two nodes. The rule reports a node with no key or several keys, and an edge with several keys.

## Severity

Error

## How to fix

Mark exactly one property of a node with `[Key]`. Remove all but one `[Key]` from an edge, or remove them all when there is at most one edge of the type between two nodes.

## Related topics

- [Graph projections](/chronicle/projections/graph-projections/)