> ## 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. # Message variable catalog > List the variables a SEND_MESSAGE template binding can reference for a journey — the same set the builder offers, and the authority on what resolves for THIS journey (when docs and this catalog disagree, trust the catalog). customer.* and person.* are offered for every trigger type (person.* is read live at send time from the identity the enrollment named — personExternalId, which event triggers always carry — and only falls back to a phone/email lookup, blank on zero or several matches, for contacts enrolled without a CDP person). The trigger-aware part is participant data: event-triggered journeys get the event payload under engagement.workflowState.* and no engagement.context.*, segment-triggered journeys get segment output columns under engagement.workflowState.*, and manual/CSV enrollment populates engagement.context.*. Bind a template placeholder to one of the returned `path` values (custom person attributes are `person.`, NOT `attributes.` — that is the DECISION/CASE condition syntax). A binding may append ONE formatting helper after a pipe: `currency:MXN` (code required), `date` or `date:long`, `sum` / `sum:field`, `count`, `fixed:N` — e.g. "engagement.nodeOutputs.fetch.body.total | currency:MXN". No chaining. `currency`/`date` are localized to the org language; `sum`/`count`/`fixed` are deliberately NOT, so they stay parseable by a DECISION comparison and valid inside a JSON body. Applied to a missing value the helper is skipped entirely, so a gap renders blank rather than "NaN" or "Invalid Date". `count` is the one to reach for before indexing an array: binding `body.buyers.0.account` on a plural array picks an arbitrary element, so gate a DECISION on `count eq 1` instead of guessing. Pass a journey id or its initiative id. ## OpenAPI ````yaml /api-reference/openapi.json get /api/v1/journeys/{journeyId}/message-variables 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/journeys/{journeyId}/message-variables: get: tags: - Journeys summary: Message variable catalog description: >- List the variables a SEND_MESSAGE template binding can reference for a journey — the same set the builder offers, and the authority on what resolves for THIS journey (when docs and this catalog disagree, trust the catalog). customer.* and person.* are offered for every trigger type (person.* is read live at send time from the identity the enrollment named — personExternalId, which event triggers always carry — and only falls back to a phone/email lookup, blank on zero or several matches, for contacts enrolled without a CDP person). The trigger-aware part is participant data: event-triggered journeys get the event payload under engagement.workflowState.* and no engagement.context.*, segment-triggered journeys get segment output columns under engagement.workflowState.*, and manual/CSV enrollment populates engagement.context.*. Bind a template placeholder to one of the returned `path` values (custom person attributes are `person.`, NOT `attributes.` — that is the DECISION/CASE condition syntax). A binding may append ONE formatting helper after a pipe: `currency:MXN` (code required), `date` or `date:long`, `sum` / `sum:field`, `count`, `fixed:N` — e.g. "engagement.nodeOutputs.fetch.body.total | currency:MXN". No chaining. `currency`/`date` are localized to the org language; `sum`/`count`/`fixed` are deliberately NOT, so they stay parseable by a DECISION comparison and valid inside a JSON body. Applied to a missing value the helper is skipped entirely, so a gap renders blank rather than "NaN" or "Invalid Date". `count` is the one to reach for before indexing an array: binding `body.buyers.0.account` on a plural array picks an arbitrary element, so gate a DECISION on `count eq 1` instead of guessing. Pass a journey id or its initiative id. operationId: journeys_message_variables parameters: - name: journeyId in: path required: true schema: $schema: https://json-schema.org/draft/2020-12/schema type: string minLength: 1 description: >- A journey id, or the initiative id (resolves to its current draft). responses: '200': description: Success content: application/json: schema: $schema: https://json-schema.org/draft/2020-12/schema type: object properties: groups: type: array items: type: object properties: id: type: string label: type: string description: type: string variables: type: array items: type: object properties: key: type: string label: type: string path: type: string description: >- Bind a placeholder to this exact value, e.g. customer.name or engagement.workflowState.plan. description: type: string required: - key - label - path additionalProperties: false required: - id - label - variables additionalProperties: false notes: description: >- Trigger-specific caveats. Present for event-triggered journeys: explains why the person.* and engagement.context.* groups are absent. type: string required: - groups 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.