---
title: "Discover custom data availability and schema"
method: GET
path: "/v1/custom-data/fields"
---

# Discover custom data availability and schema

`GET /v1/custom-data/fields`

Whether custom data is enabled for the calling account, and the schema of the exposed fields. Safe capability probe: a key without custom data receives 200 with custom_data_enabled: false, never 403. Call this before using the custom-data endpoints.

## Response `200`

Capability flag and field schema

- CustomDataFieldsResponse
  - `custom_data_enabled` boolean, required
  - `source_integration` 'salesforce' | 'hubspot' — Present when enabled
  - `fields` CustomDataField[], required
    - `field_key` string — Key used inside custom_data objects and in POST /v1/custom-data/lookup field projections
    - `display_name` string, nullable
    - `data_type` string, nullable — e.g. number, boolean, text — from the account’s CRM configuration
  - `total_records` integer — Estimated record count (present when enabled)
  - `message` string — Present when not enabled

## Other responses

- `401` — Invalid or missing API key
- `429` — Too many requests. Check X-RateLimit-Remaining and Retry-After headers.
- `503` — The account’s custom data configuration is invalid. Contact support; retrying will not help.

---

[API](https://skmtc.net/runalphaloops/apis/alphaloops-fmcsa-carrier-data-api.md) · [All operations](https://skmtc.net/runalphaloops/apis/alphaloops-fmcsa-carrier-data-api/llms.txt) · [OpenAPI document](https://skmtc-service-staging.skmtc.workers.dev/v1/apis/runalphaloops/alphaloops-fmcsa-carrier-data-api/revisions/ae58c064a7af/schema)