> ## Documentation Index > Fetch the complete documentation index at: https://attend.hackclub.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Preview a message > Step two of the composer: how many people the message would reach (and up to 20 of their names), and how it renders on each channel it uses. Channel renderings are `null` for channels the message doesn't use. Only drafts and scheduled messages can be previewed. ## OpenAPI ````yaml /openapi.yml get /events/{event_id}/messages/{id}/preview openapi: 3.0.3 info: title: Attend API version: v1 description: > REST API for [Attend](https://attend.hackclub.com), Hack Club's event management platform. The API is used by the Attend mobile app and by trusted server-to-server integrations. ## Authentication Almost every endpoint requires a bearer token: ``` Authorization: Bearer ``` Four kinds of token are accepted: - **Mobile token** — issued to a signed-in user by `POST /session`. Sets the current user. May return the response header `X-Token-Refresh-Recommended: true` when the token is nearing expiry; call `POST /session/refresh` to rotate it. - **Global API token** — a superadmin-issued token. Only honoured while its owner is still a global admin. Sets the current user. May be **scoped** when issued, in which case it reaches only the endpoints that accept that scope and returns `403` everywhere else, read-only endpoints included. An unscoped token carries its owner's full access. Scopes are noted on the endpoints that accept them: `bans:write` and `support:read`. - **Series API key** — one key for a whole event series, issued from **Series → API Keys** in the dashboard by a series owner. Does **not** set a current user. It acts as an event API key on *every* event in its series, and it is the only credential that can create an event. Scopes do not apply — a series key's reach is its series. See the **Series** section. - **Event API key** — per-event key (`EventApiToken`, or the legacy `Event#api_key`). Does **not** set a current user, so it only works on the subset of endpoints that don't require one (participant `lookup`, `roster`, `create`, `update` and `delete`, event setup, event staff, and the travel calendar). Missing or invalid credentials return `401 { "error": "Unauthorized" }`. ### What an API key cannot do Neither key kind sets a current user, so endpoints that must attribute work to a person stay closed to both — regardless of how broad the key is. A series key is wider in *reach* (more events), never in *depth*: | Endpoint | Series key | Event key | | --- | --- | --- | | `GET/POST /series/…` | ✅ its own series | ❌ `403` | | `POST /series/{id}/events` | ✅ its own series | ❌ `403` | | Participant `lookup`, `roster`, `create` | ✅ any event in the series | ✅ its own event | | `PATCH`/`DELETE` a participant | ✅ any event in the series | ✅ its own event | | `/events/{id}/setup/…` and `/events/{id}/staff` | ✅ any event in the series | ✅ its own event | | `GET /events/{id}/travel` | ✅ any event in the series | ✅ its own event | | `GET /events/{id}/participants` (full payload) | ❌ `403` | ❌ `403` | | Notes, scans, scan contexts, Slack blasts, NFC badges | ❌ `403` | ❌ `403` | | `/events/{id}/messages/…` and `/events/{id}/incidents/…` | ❌ `403` | ❌ `403` | | `GET /incident_reports/options` and `POST /incident_reports` | ❌ `403` | ❌ `403` | | `GET /messages` and `GET /messages/{id}` (inbox) | ❌ `403` | ❌ `403` | Either key can be revoked without credentials by POSTing its own secret to `POST /tokens/revoke`; Attend emails the key's owner (or, if their account is gone, the series owners) when that happens. ## Conventions - All timestamps are ISO 8601 strings and may be `null` where noted. - Errors use the envelope `{ "error": "" }`. - `:event_id` path segments accept a numeric id or the event slug on the participants, setup, and staff endpoints; other endpoints accept the numeric id only. - A caller that may *write* a field cannot always *read* it back: dates of birth, phone numbers, addresses and the details of the people around a participant are omitted (not nulled) for API keys and PII-restricted roles, in responses to writes just as in responses to reads. > **Note:** Inbound webhook receivers (Postmark, Help Scout, DocuSeal, > Slack events) also live under `/api/v1` but are called by third parties, > not by API consumers, and are not documented here. servers: - url: https://attend.hackclub.com/api/v1 description: Production - url: http://localhost:3000/api/v1 description: Local development security: - bearerAuth: [] tags: - name: Authentication description: Obtain, refresh, and revoke mobile bearer tokens. - name: Account description: The authenticated user's profile and accessible events. - name: Series description: >- Event series, and the events inside one, addressed with a single series API key. Creating an event lives here — an event has to belong to a series, and only a series key names one unambiguously. - name: Event Setup description: >- The tail of the setup wizard — waiver configuration and taking an event out of draft — for events created through the API. - name: Event Staff description: Who has access to an event, and what they can do there. - name: Participants description: Participant registrations for an event. - name: Notes description: Staff notes on a participant's registration. - name: Scans description: QR / NFC / manual scans and check-in. - name: Scan Contexts description: The scan stations configured for an event. - name: Stays description: >- An event's stays — during the event, the night before, the night after — and the roster of who's staying for each list-only stay. Built for a shop that sells the night: add buyers to the roster on purchase, remove them on refund. Accepts an event or series API key, or a global token scoped to `rooming:write`. - name: Travel Calendar description: Chronological participant travel and pickup operations. - name: Slack Blasts description: Broadcast Slack messages to an event's participants. - name: Messages description: >- Compose, preview, schedule and send an organizer broadcast over Slack, email, SMS and push, and follow its deliveries. - name: Incidents description: >- An event's incident log — logging, sharing, commenting on and escalating incidents to Hack Club HQ. - name: NFC Badges description: Provision and manage participant NFC badges. - name: Push Tokens description: Register device push-notification tokens. - name: Inbox description: The organizer messages delivered to the signed-in participant. - name: Incident Reports description: File a confidential incident report straight to Hack Club HQ. - name: Bans description: The app-wide ban list. Global admins only. - name: Travel description: >- Airport and flight lookups. These endpoints authenticate with the web session cookie (Devise), not a bearer token. paths: /events/{event_id}/messages/{id}/preview: get: tags: - Messages summary: Preview a message description: >- Step two of the composer: how many people the message would reach (and up to 20 of their names), and how it renders on each channel it uses. Channel renderings are `null` for channels the message doesn't use. Only drafts and scheduled messages can be previewed. parameters: - $ref: '#/components/parameters/EventId' - $ref: '#/components/parameters/MessageId' responses: '200': description: The preview. content: application/json: schema: type: object properties: preview: $ref: '#/components/schemas/MessagePreview' '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/MessagesForbidden' '404': $ref: '#/components/responses/NotFound' '422': description: The message has already been sent. content: application/json: schema: $ref: '#/components/schemas/Error' components: parameters: EventId: name: event_id in: path required: true schema: type: string description: Event id or slug. MessageId: name: id in: path required: true schema: type: string format: uuid description: The message id. Must belong to the event in the path. schemas: MessagePreview: type: object properties: total_count: type: integer description: Estimated number of recipients. recipient_names: type: array description: Up to 20 of them. items: type: string audience_label: type: string channel_labels: type: string example: Email, SMS (Twilio) channels: type: array items: type: string slack_text: type: string nullable: true email_subject: type: string nullable: true body_html: type: string sms_text: type: string nullable: true sms_length: type: integer sms_segments: type: integer description: 160-character SMS segments. scheduled_at: type: string format: date-time nullable: true scheduled_in_future: type: boolean description: True when `send_now` would schedule rather than send. Error: type: object properties: error: type: string example: Unauthorized responses: Unauthorized: description: Missing or invalid credentials. content: application/json: schema: $ref: '#/components/schemas/Error' MessagesForbidden: description: >- The caller has no access to this event, or is an API key (`API key is not authorized for messages`). content: application/json: schema: $ref: '#/components/schemas/Error' NotFound: description: Event or record not found. content: application/json: schema: $ref: '#/components/schemas/Error' securitySchemes: bearerAuth: type: http scheme: bearer description: >- Mobile token, global API token, series API key, or event API key. See Authentication above for which endpoints each one reaches. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.