> ## Documentation Index > Fetch the complete documentation index at: https://docs.useboom.ai/llms.txt > Use this file to discover all available pages before exploring further. # Upsert object > Create or update a custom object by type and external id. The type must already exist. By default `attributes` is REPLACED wholesale — pass `mode: 'merge'` to add or change a subset without deleting the rest, and `createMissing: false` to update only when the object already exists. ## OpenAPI ````yaml /api-reference/openapi.json post /api/v1/cdp/custom-objects openapi: 3.1.0 info: title: Boom API version: 1.0.0 description: >- Boom's public REST API — one uniform surface over every platform capability. CDP: upsert people and custom objects, define object and relationship types, link and unlink relationships, and record behavioral events — one record per request or up to 1000 per request via the `/batch` endpoints. Segments: read (list, read, membership) and full authoring — discover the filterable catalog, validate a filter, create and update segments, preview match counts, and trigger evaluation. Initiatives: create and configure outreach initiatives, link WhatsApp templates, drive the lifecycle (launch, cancel, archive), and read collected-data summaries. Participants: enroll people into an active initiative, track their status, read conversation transcripts, and stop outreach. Journeys: read-only access to always-on message flows and their metrics. WhatsApp templates: list your WhatsApp numbers and list, read, and create message templates. The same capabilities are exposed as MCP tools with identical schemas. servers: - url: https://www.useboom.ai description: Production - url: https://dev.useboom.ai description: Development (sandbox — use a development organization API key) security: - bearerAuth: [] paths: /api/v1/cdp/custom-objects: post: tags: - CDP Custom Objects summary: Upsert object description: >- Create or update a custom object by type and external id. The type must already exist. By default `attributes` is REPLACED wholesale — pass `mode: 'merge'` to add or change a subset without deleting the rest, and `createMissing: false` to update only when the object already exists. operationId: cdp_custom_objects_upsert requestBody: required: true content: application/json: schema: $schema: https://json-schema.org/draft/2020-12/schema type: object properties: type: type: string minLength: 1 maxLength: 255 description: >- The custom object type name. Must already exist (create it with the types endpoint) — unknown types are rejected. externalId: type: string minLength: 1 maxLength: 255 description: >- Your stable identifier for this object within its type (idempotency key). displayName: description: Human-readable label for the object. type: string minLength: 1 maxLength: 255 attributes: description: >- Free-form custom traits. Full-replace by default — omitted keys are deleted. Pass mode:'merge' to overlay only what you send. type: object propertyNames: type: string maxLength: 255 additionalProperties: {} mode: default: replace description: >- How `attributes` is applied. 'replace' (default) swaps the whole blob — any stored attribute you leave out is DELETED. 'merge' overlays the keys you send onto the stored ones and leaves the rest untouched, which is what you want when adding or changing a subset. type: string enum: - replace - merge createMissing: default: true description: >- When false, objects that do not already exist are skipped and reported in `skipped` instead of being created. Use it when working from a list that may not match, so a bad id enriches nothing rather than inventing an object. type: boolean required: - type - externalId responses: '200': description: Success content: application/json: schema: $schema: https://json-schema.org/draft/2020-12/schema type: object properties: type: type: string externalId: type: string created: type: boolean required: - type - externalId - created additionalProperties: false '400': description: Validation failed or the request cannot proceed. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '401': description: Missing, malformed, or revoked API key. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '404': description: The resource does not exist in this organization. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '409': description: >- Conflicts with the current state (duplicates, wrong lifecycle state). content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '422': description: The request is well-formed but semantically invalid. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '429': description: Rate limit exceeded — retry after `Retry-After`. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '500': description: Internal server error. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '503': description: Transient error — retry with a narrower request. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error components: securitySchemes: bearerAuth: type: http scheme: bearer description: 'Organization API key, sent as `Authorization: Bearer boom_org_...`.' ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.