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url: /docs/api/core/functions/deriveExternalId.md
---
[**@kaiord/core**](../README.md)

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[@kaiord/core](../README.md) / deriveExternalId

# Function: deriveExternalId()

> **deriveExternalId**(`input`): `string`

Defined in: [packages/core/src/domain/ingest/derive-external-id.ts:11](https://github.com/pablo-albaladejo/kaiord/blob/3eacbe62ef72342d970523967cc5155b5935bb85/packages/core/src/domain/ingest/derive-external-id.ts#L11)

Derives a stable external id for a health record from its payload +
measuredAt timestamp.

The `k1:` prefix is a version tag: if the hash projection ever changes,
the prefix can be bumped to `k2:` so downstream migration code can
distinguish old ids from new ones without inspecting content.

## Parameters

### input

#### measuredAt

`string`

#### payload

`Record`<`string`, `unknown`>

## Returns

`string`