> ## Documentation Index > Fetch the complete documentation index at: https://docs.getaptly.com/llms.txt > Use this file to discover all available pages before exploring further. # Add a mirror field > Adds a field to the board that mirrors a field of another board. The new field takes the target field's type (and, for select types, a copy of its option list), is named `Mirror ` unless you supply `name`, and is read-only unless you set `readOnly: false`. This only adds the field - the same as the Aptly app. A card shows a mirrored value once it is linked to a card on the target board (for example through a related-cards field) and is next saved; existing cards are not backfilled when the field is added. Requires `update` permission and the key's "Edit Boards" access (off by default). A key's board allowlist applies to **both** boards: the target board must be one the key can access and must be API-enabled. The target field must be one of `string`, `text`, `rich-text`, `address`, `email`, `url`, `datetime-local`, `date`, `number`, `percent`, `stageselect`, `singleselect`, `multiselect`, `tags`, `boolean`, `person`, `persons`, `relatedAptlets`, `files`, `file`, `money`, `user` or `lockAlias`, and can't itself be a mirror field. Mirroring the same target field twice on one board returns `409`. ## OpenAPI ````yaml /openapi.yaml post /api/board/{boardId}/configuration/mirror-fields openapi: 3.0.3 info: title: Aptly API version: '1.1' description: | The Aptly API lets external systems work with boards, contacts, inboxes, tasks, files, and other Aptly resources. Most endpoints accept an API key in the `x-token` header. Some endpoints also accept a delegate token or partner bearer token, as shown in each operation's security requirements, and explicitly public endpoints require no credential. API keys are scoped to a company and may be restricted to specific boards and read, insert, or update permissions; requests outside those restrictions receive a 403 `FORBIDDEN` response. servers: - url: https://core-api.getaptly.com description: Production security: - ApiKeyHeader: [] paths: /api/board/{boardId}/configuration/mirror-fields: post: tags: - Board summary: Add a mirror field description: > Adds a field to the board that mirrors a field of another board. The new field takes the target field's type (and, for select types, a copy of its option list), is named `Mirror ` unless you supply `name`, and is read-only unless you set `readOnly: false`. This only adds the field - the same as the Aptly app. A card shows a mirrored value once it is linked to a card on the target board (for example through a related-cards field) and is next saved; existing cards are not backfilled when the field is added. Requires `update` permission and the key's "Edit Boards" access (off by default). A key's board allowlist applies to **both** boards: the target board must be one the key can access and must be API-enabled. The target field must be one of `string`, `text`, `rich-text`, `address`, `email`, `url`, `datetime-local`, `date`, `number`, `percent`, `stageselect`, `singleselect`, `multiselect`, `tags`, `boolean`, `person`, `persons`, `relatedAptlets`, `files`, `file`, `money`, `user` or `lockAlias`, and can't itself be a mirror field. Mirroring the same target field twice on one board returns `409`. operationId: addBoardMirrorField parameters: - name: boardId in: path required: true description: The board that gets the mirror field. schema: type: string requestBody: required: true content: application/json: schema: type: object required: - targetBoardUuid - targetFieldUuid properties: targetBoardUuid: type: string description: The uuid of the board to mirror a field from. targetFieldUuid: type: string description: The uuid of the field on that board to mirror. name: type: string description: >- Display name for the new field. Defaults to `Mirror `. readOnly: type: boolean description: >- Whether users may edit the mirrored value on this board. Defaults to `true`. example: targetBoardUuid: deals targetFieldUuid: rent name: Deal rent responses: '201': description: The created field. content: application/json: schema: type: object properties: data: $ref: '#/components/schemas/BoardField' example: data: uuid: Qk3x9TnWc2LmPa8vR name: Deal rent type: money optional: true pinned: false position: 12 readOnly: true metricField: false mirrorTarget: targetAptletUuid: deals targetFieldUuid: rent '400': description: >- `VALIDATION_ERROR` (per-field `meta.issues`), or the target field's type can't be mirrored, or the target field is itself a mirror field. content: application/json: schema: $ref: '#/components/schemas/ValidationError' '401': description: Invalid or missing API key. '403': description: >- The key lacks `update` permission or the "Edit Boards" access, either board is outside the key's board allowlist, or the board or target board isn't API-enabled. '404': description: The board, the target board or the target field was not found. '409': description: >- The board already mirrors that target field. `meta.fieldUuid` is the existing mirror field. security: - ApiKeyHeader: [] - PartnerBearer: [] components: schemas: BoardField: type: object properties: uuid: type: string description: >- Unique field identifier — use this as the key when reading/writing card data. name: type: string description: Display name of the field. type: type: string description: >- Field type. Fields created through the API use one of the types in `NewBoardFieldType` (`string`, `text`, `rich-text`, `number`, `money`, `percent`, `multiplier`, `boolean`, `date`, `datetime-local`, `email`, `emails`, `tel`, `phones`, `url`, `address`, `person`, `persons`, `user`, `file`, `files`, `heroImage`, `embedVideo`, `stringList`, `tags`, `singleselect`, `multiselect`, `checkboxlist`). Mirror fields (a copy of another board's field) are added with `POST /api/board/{boardId}/configuration/mirror-fields` and take the mirrored field's type. Boards built in the Aptly app can also contain relational and system types, e.g. `stageselect`, `sourceselect`, `relatedAptlets`, `mirror`, `mirror-contact`, `location`, `unit`, `board`, `calculation`, `ai-computed`, `cardId`, `daysOpened`, `timeSince`, `qualified`, `lostReason`, `lostDetails`, `relatedEvents`, `relatedDocuments`, `contactType`, `teams`. position: type: integer description: Display order (zero-based). optional: type: boolean description: Whether the field is optional on cards. archived: type: boolean description: Whether the field has been archived (hidden from the UI). ValidationError: type: object description: > Returned with HTTP 400 when the request body fails shape validation (wrong type, missing required field, malformed email/phone number, value out of bounds). `meta.issues` lists every offending field. properties: error: type: object properties: code: type: string enum: - VALIDATION_ERROR message: type: string example: One or more fields are invalid meta: type: object properties: issues: type: array items: type: object properties: field: type: string description: >- Dotted path to the offending property (for example `to.0.value`); empty for a problem with the body as a whole. example: to.0.value code: type: string description: >- Machine-readable issue code (for example `invalid_type`, `invalid_format`, `too_small`). example: invalid_format message: type: string example: must be a valid email address requestId: type: string securitySchemes: ApiKeyHeader: type: apiKey in: header name: x-token PartnerBearer: type: http scheme: bearer description: 'Partner token. Format: `Authorization: Bearer `' ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.