# Create a dynamic Segment

`POST /v1/segments`

- Authentication: required (Bearer token)
- Required scope: `api.segments.manage`

Creates a managed Segment definition and evaluates its predicate before
returning, so the `201` carries the number of contacts it matches:
`member_count` with `evaluation: "complete"`, or a `null` count with
`evaluation: "queued"` when the evaluation exceeded its budget and a
background reconcile took over. A null count is never a zero — zero
means the predicate matched nobody.

`key` is optional and defaults to a slug of the name; it is the stable
org-unique handle every other call addresses the Segment by, and it is
immutable afterwards. A key already in use returns `409 conflict`.

A predicate that does not compile is still saved, with
`status: "invalid"` and the reason — work in progress is not thrown
away — but a predicate that names something the org does not have
returns `422 validation_failed` positioned at the fault, with the org's
real attribute names in `candidates`. Lint first with
`POST /v1/segments/validate` and size it with `POST /v1/segments/preview`.

Saving a Segment mails nobody: a broadcast or a workflow is what sends.

## Request body

Content type: `application/json`

```json
{
  "name": "string",
  "key": "string",
  "description": "string",
  "source": "string",
  "expected_content_hash": "string"
}
```

## Example request

```bash
curl -X POST 'https://api.sendops.dev/v1/segments' \
  -H "Authorization: Bearer $SENDOPS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"name":"string","key":"string","description":"string","source":"string","expected_content_hash":"string"}'
```

## Responses

### 201 — The created Segment, with its evaluated member count

Content type: `application/json`

```json
{
  "id": "00000000-0000-0000-0000-000000000000",
  "name": "string",
  "key": "string",
  "description": "string",
  "source": "string",
  "profile_version": 0,
  "eval_class": "incremental",
  "status": "active",
  "member_count": 0,
  "evaluation": "complete",
  "eval_warning": "string",
  "eval_warning_at": "2026-05-17T20:00:00Z",
  "last_evaluated_at": "2026-05-17T20:00:00Z",
  "content_hash": "string",
  "warnings": [
    "string"
  ],
  "requires": [
    {
      "kind": "template",
      "key": "string",
      "status": "ok",
      "detail": "string",
      "fix": "string"
    }
  ],
  "created_at": "2026-05-17T20:00:00Z",
  "updated_at": "2026-05-17T20:00:00Z"
}
```

### 401 — Missing, malformed, or unknown API key

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 403 — Key lacks the required scope or plan limit violated

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 409 — The mutation is rejected by a state rule rather than a bad request. The
`code` is `conflict`.

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 422 — A query parameter, path value or body field failed validation.

The body is a `validation_failed` Problem. When the refusal is about a
reference — a segment key, template slug, topic or attribute name the
organization does not have — it additionally carries `validation_code`,
`field`, `line`/`column`, `missing`, `candidates` and `next_step`, so a
client can correct the call without a second round of guessing. See
`ValidationProblem`.

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ],
  "validation_code": "invalid_syntax",
  "field": "string",
  "line": 0,
  "column": 0,
  "missing": [
    {
      "kind": "segment",
      "key": "string"
    }
  ],
  "candidates": {},
  "next_step": "string"
}
```

### 429 — Per-org rate limit exceeded

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 500 — Unexpected server-side failure. The `code` is `internal_error`. The
`request_id` field can be quoted to SendOps support to investigate.

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```