> ## Documentation Index > Fetch the complete documentation index at: https://apidoc.mailercloud.com/llms.txt > Use this file to discover all available pages before exploring further. # List Campaign Opens > Get a paginated list of contacts who opened a specific campaign. Each row carries the contact's encrypted id, email, name, the tags currently assigned to the contact, the lists the contact currently belongs to (with their ids and names), and the time of the open in your account timezone. Each contact appears at most once in the response. If a contact opened the campaign multiple times, the time shown is the most recent open. ## OpenAPI ````yaml /openapi-v1.json post /campaign/{id}/opens openapi: 3.1.0 info: title: Mailercloud Marketing API version: 1.0.0 description: >- Campaigns, contacts, lists, segments, automations, and webhooks for the Mailercloud Marketing Platform. servers: - url: https://cloudapi.mailercloud.com/v1 security: - apiKey: [] tags: - name: Campaigns - name: Contacts - name: Lists - name: Tags - name: Segments - name: Custom Properties - name: Senders - name: Templates - name: Automations - name: Webhooks - name: Webforms - name: Inbox Tracker - name: Account paths: /campaign/{id}/opens: post: tags: - Campaigns summary: List Campaign Opens description: >- Get a paginated list of contacts who opened a specific campaign. Each row carries the contact's encrypted id, email, name, the tags currently assigned to the contact, the lists the contact currently belongs to (with their ids and names), and the time of the open in your account timezone. Each contact appears at most once in the response. If a contact opened the campaign multiple times, the time shown is the most recent open. operationId: list-campaign-opens parameters: - name: id in: path required: true description: Encrypted campaign id schema: type: string - name: Content-Type in: header required: true description: Request body type schema: type: string default: application/json requestBody: required: true content: application/json: schema: type: object required: - page - limit properties: page: type: integer minimum: 1 description: |- Page number (1-indexed). Minimum: 1 limit: type: integer minimum: 1 maximum: 100 description: |- Maximum rows per page. Minimum: 1 Maximum: 100 date_from: type: string description: >- Optional. Only return opens on or after this date. Format `YYYY-MM-DD`, interpreted in your account timezone. date_to: type: string description: >- Optional. Only return opens on or before this date. Format `YYYY-MM-DD`, interpreted in your account timezone. Must be on or after `date_from`. examples: Example-1---Default: value: page: 1 limit: 25 Example-2---With-date-filter: value: page: 1 limit: 50 date_from: '2026-01-01' date_to: '2026-01-31' responses: '200': description: OK content: application/json: schema: type: object properties: campaign: type: object properties: name: type: string description: Campaign name. subject_line: type: string description: Campaign subject line. created_date: type: string description: >- Campaign creation date and time. Format: `YYYY-MM-DD HH:mm:ss` in your account timezone. data: type: array items: type: object properties: contact_id: type: string description: >- Encrypted contact id (use with `GET /v1/contacts/{id}`). email: type: string description: Contact email. first_name: type: string description: Contact first name. last_name: type: string description: Contact last name. tags: type: array items: type: string description: >- Names of the tags currently assigned to the contact. Empty array when the contact has no tags. lists: type: string description: >- Comma-separated encrypted ids of the lists the contact currently belongs to. The literal string `"no lists"` when the contact belongs to no lists. list_name: type: string description: >- Comma-separated names of the lists the contact currently belongs to. Each list appears only once. The literal string `"no lists"` when the contact belongs to no lists. created_date: type: string description: >- Time of the open. Format: `YYYY-MM-DD HH:mm:ss` in your account timezone. total: type: integer description: >- Total number of contacts who opened the campaign, ignoring pagination. examples: Example-1---With-rows: value: campaign: name: May newsletter subject_line: Big update inside created_date: '2026-05-10 11:30:00' data: - contact_id: SuwESEuwZZ email: alice@example.com first_name: Alice last_name: Anderson tags: - VIP - Newsletter lists: SuSwZS,KkfHZw list_name: Newsletter Subscribers, Beta Testers created_date: '2026-05-15 08:42:11' - contact_id: SuwESEuwZf email: bob@example.com first_name: Bob last_name: '' tags: [] lists: no lists list_name: no lists created_date: '2026-05-15 09:14:02' total: 1234 Example-2---Empty-result: value: campaign: name: May newsletter subject_line: Big update inside created_date: '2026-05-10 11:30:00' data: [] total: 0 '400': description: Bad Request - validation failure content: application/json: schema: type: object properties: errors: type: array items: type: object properties: field: type: string message: type: string examples: Page-required: value: errors: - field: page message: Page is a required field Limit-out-of-range: value: errors: - field: limit message: Limit must be 100 or less Bad-date-format: value: errors: - field: date_from message: Invalid date_from Date-range-invalid: value: errors: - field: date_to message: date_to must be on or after date_from Malformed-JSON: value: errors: - field: '' message: Invalid json '401': description: Unauthorized - missing or invalid API key content: application/json: schema: type: object properties: errors: type: array items: type: object properties: field: type: string message: type: string examples: Example-1: value: errors: - field: '' message: Authorization failed '404': description: Not Found - the campaign id does not exist in your account content: application/json: schema: type: object properties: errors: type: array items: type: object properties: field: type: string message: type: string examples: Example-1: value: errors: - field: id message: Campaign not found '429': description: Too Many Requests - rate limit exceeded content: application/json: schema: type: object properties: message: type: string examples: Example-1: value: message: Too Many Requests '500': description: Internal Server Error content: application/json: schema: type: object properties: message: type: string examples: Example-1: value: message: >- Sorry, we are experiencing some technical difficulties. Please try after some time. components: securitySchemes: apiKey: type: apiKey in: header name: Authorization description: >- Your Mailercloud API key (plain text, no Bearer prefix). Create keys in Settings → API. ````