> ## Documentation Index
> Fetch the complete documentation index at: https://docs.kairn.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Write memory

> Write key-value pairs to a user's memory. Set a key's value to `null` to delete it. Writes are merged into existing memory — keys not in `delta` are unchanged.



## OpenAPI

````yaml PATCH /v1/memory/{userId}
openapi: 3.1.0
info:
  title: Kairn API
  version: 1.0.0
  description: >-
    The Kairn API. All requests require an `X-API-Key` header with your tenant
    API key.
servers:
  - url: https://api.kairn.sh
    description: Production
security:
  - ApiKey: []
tags:
  - name: Agent
    description: Invoke agents and stream responses.
  - name: Memory
    description: Read and write per-user agent memory.
  - name: Souls
    description: Manage agent identities.
  - name: Skills
    description: Manage custom skills (instructions and webhook tools).
  - name: Mandates
    description: Schedule autonomous agent tasks.
  - name: Invocations
    description: Inspect past agent runs.
  - name: Sessions
    description: Access multi-turn conversation history.
  - name: Audit
    description: Audit log for all agent activity.
paths:
  /v1/memory/{userId}:
    patch:
      tags:
        - Memory
      summary: Write memory
      description: >-
        Write key-value pairs to a user's memory. Set a key's value to `null` to
        delete it. Writes are merged into existing memory — keys not in `delta`
        are unchanged.
      operationId: memory-set
      parameters:
        - name: userId
          in: path
          required: true
          schema:
            type: string
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - role
                - delta
              properties:
                role:
                  type: string
                  example: default
                delta:
                  type: object
                  additionalProperties:
                    type: string
                    nullable: true
                  example:
                    plan: pro
                    old_key: null
      responses:
        '200':
          description: Memory written.
          content:
            application/json:
              schema:
                type: object
                properties:
                  status:
                    type: string
                    example: ok
                  updated:
                    type: array
                    items:
                      type: string
components:
  securitySchemes:
    ApiKey:
      type: apiKey
      in: header
      name: X-API-Key

````

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