# Start cloud runtime

Start a browser profile as a cloud runtime.
- **Preconditions**: the profile must exist in your team and must not be end-to-end encrypted or mid-transfer. **A proxy is required** and its reachability is checked before the start is accepted. The browser kernel must be one the cloud browser supports, which rules out Firefox. Team open limits are enforced, and on deployments with cloud-browser billing enabled the AI credit balance is checked too.
- **One run per profile**: a member may hold only one active run for a profile. When the team enables the security lock, another member's run blocks yours.
- **Completion**: **accepted, not complete.** `data` is empty; the runtime is provisioned asynchronously. Poll `/cloudbrowser/page` until `cloudBrowserStatus` is `RUNNING`, then call `/cloudbrowser/connect` for `cdpUrl`. A start can be accepted and still fail later, which surfaces on that page.
- **Concurrency**: concurrent starts for one profile are serialized by a lock; the loser is rejected rather than queued.
- **Retry**: after a timeout, read `/cloudbrowser/page` — do not resend.

Documented business errors: `19039`, `19065`, `40001`, `40003`, `40015`, `40016`, `40021`, `40023`, `40024`, `40025`, `40026`, `40027`, `40028`, `40029`, `40037`. See [Error Codes](../Getting%20Started/error-codes.md) for what each code means. Any operation can additionally return the common codes.

Endpoint: POST /api/cloudbrowser/start
Version: 2026-09-05

## Request fields (application/json):

  - `envId` (string, required)
    Browser profile (environment) ID. Serialized as a decimal string to avoid JavaScript
precision loss on 64-bit integers.
    Example: 1800000000000001

## Response 200:

  - `200` (unknown)
    Success

## Response 200 fields (application/json):

  - `code` (integer, required)
    Return result code. `0` means success; other codes indicate exceptions.
    Example: 0

  - `msg` (string | null, required)
    Error message. Usually `null` on success.
    Example: null

  - `requestId` (string)
    Operation request ID. This field may be present when the request passes through the API gateway.
    Example: 1d4f3ea968664593860b94b35d4ebf5e

  - `data` (null)
    Example: null