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# Flows · Workflows · Start a workflow run and return its run ID

POST https://api.simplified.com/api/v1/workflows/workflows/{workflow_id}/start
Content-Type: application/json

Starts one execution of a published workflow and returns immediately.

**This does not wait for the run to finish.** Workflows routinely take minutes
and can take hours. The response is `{workflow_id, correlation_id}` where —
despite the name — **`workflow_id` is the new RUN ID**, a UUID.

`input` keys must match the workflow's declared input schema. Keys that do not
match are rejected or silently dropped, and a dropped key means the run
proceeds without it. Pass `{}` when the workflow declares no inputs. Do not
include a `context` key; the server injects workspace and user context itself.

Side effects are real and often external — workflows send email, post to
Slack, publish content, and consume workspace credits. Do not start one
speculatively. Pass `idempotency_key` when a retry on your side must not
produce a second run.

Fails with 400 if the workflow has never been published, and 429 if the
workspace is out of credits.

`resource: workflow://run-control` covers polling and the two-ID confusion.

Reference: https://docs.simplified.com/api-reference/workflows/runs/start-workflow

## Authentication

- `Authorization` header (required) (prefixed with ` Api-Key   `) — Header authentication of the form `Api-Key  <token>`
- `Authorization` header (bearer token, required) — Bearer authentication of the form `Bearer <token>`, where token is your auth token.

## Request

### Path parameters

- `workflow_id` (integer, required) — Numeric workflow-definition ID from `flows_listWorkflows`. Not a run ID.

### Query parameters

- `expand` (string, optional) — Set to `token` to also receive a scoped JWT that can read this run's details without full credentials.

### Body (application/json)

This endpoint expects a StartWorkflowRequest.

- `input` (map from string to any, required) — Input parameters for this run, as a flat object. The accepted keys and their types are given by the `inputs` JSON Schema on the workflow returned by `flows_listWorkflows` — read it first rather than guessing. Pass `{}` when the workflow declares no inputs. Do not include a `context` key; the server injects workspace/user context itself.
- `version` (integer, optional) — Published version to run. Omit to run the latest published version, which is almost always what you want.
- `correlation_id` (string, optional) — Your own identifier for correlating this run later. Auto-generated when omitted. Useful when you start many runs and need to match results back to your own records.
- `idempotency_key` (string, optional) — Client-supplied key that lets the server collapse duplicate starts. Set this when a retry on your side must not produce a second run.
- `idempotency_strategy` (string, optional) — How to behave when `idempotency_key` matches an existing run. Only meaningful alongside `idempotency_key`.
- `priority` (integer, optional) — Execution priority. Leave unset unless told otherwise.
- `task_to_domain` (map from string to any, optional) — Advanced routing — pins named tasks to specific worker domains. Leave unset unless you are debugging worker placement.

## Response

### 200

Run started. `workflow_id` in the body is the RUN ID.

## Errors

### 400 Bad Request Error

Workflow is not published, or input failed validation.

- `any`

### 404 Not Found Error

No such workflow in this workspace.

- `any`

### 429 Too Many Requests Error

Workspace credit quota exhausted.

- `any`

## Examples

### Workflow whose inputs schema declares a single `topic` string

**Request**

```json
{
  "input": {
    "topic": "Q3 product launch"
  }
}
```

**Response**

```json
{}
```

**SDK Code**

```python Workflow whose inputs schema declares a single `topic` string
import requests

url = "https://api.simplified.com/api/v1/workflows/workflows/1/start"

payload = { "input": { "topic": "Q3 product launch" } }
headers = {
    "Authorization": "Api-Key  <apiKey>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript Workflow whose inputs schema declares a single `topic` string
const url = 'https://api.simplified.com/api/v1/workflows/workflows/1/start';
const options = {
  method: 'POST',
  headers: {Authorization: 'Api-Key  <apiKey>', 'Content-Type': 'application/json'},
  body: '{"input":{"topic":"Q3 product launch"}}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go Workflow whose inputs schema declares a single `topic` string
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.simplified.com/api/v1/workflows/workflows/1/start"

	payload := strings.NewReader("{\n  \"input\": {\n    \"topic\": \"Q3 product launch\"\n  }\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Api-Key  <apiKey>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby Workflow whose inputs schema declares a single `topic` string
require 'uri'
require 'net/http'

url = URI("https://api.simplified.com/api/v1/workflows/workflows/1/start")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Api-Key  <apiKey>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"input\": {\n    \"topic\": \"Q3 product launch\"\n  }\n}"

response = http.request(request)
puts response.read_body
```

```java Workflow whose inputs schema declares a single `topic` string
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.simplified.com/api/v1/workflows/workflows/1/start")
  .header("Authorization", "Api-Key  <apiKey>")
  .header("Content-Type", "application/json")
  .body("{\n  \"input\": {\n    \"topic\": \"Q3 product launch\"\n  }\n}")
  .asString();
```

```php Workflow whose inputs schema declares a single `topic` string
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.simplified.com/api/v1/workflows/workflows/1/start', [
  'body' => '{
  "input": {
    "topic": "Q3 product launch"
  }
}',
  'headers' => [
    'Authorization' => 'Api-Key  <apiKey>',
    'Content-Type' => 'application/json',
  ],
]);

echo $response->getBody();
```

```csharp Workflow whose inputs schema declares a single `topic` string
using RestSharp;

var client = new RestClient("https://api.simplified.com/api/v1/workflows/workflows/1/start");
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Api-Key  <apiKey>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"input\": {\n    \"topic\": \"Q3 product launch\"\n  }\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift Workflow whose inputs schema declares a single `topic` string
import Foundation

let headers = [
  "Authorization": "Api-Key  <apiKey>",
  "Content-Type": "application/json"
]
let parameters = ["input": ["topic": "Q3 product launch"]] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api.simplified.com/api/v1/workflows/workflows/1/start")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```

### Workflow that declares no inputs

**Request**

```json
{}
```

**Response**

```json
{}
```

**SDK Code**

```python Workflow that declares no inputs
import requests

url = "https://api.simplified.com/api/v1/workflows/workflows/1/start"

payload = {}
headers = {
    "Authorization": "Api-Key  <apiKey>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript Workflow that declares no inputs
const url = 'https://api.simplified.com/api/v1/workflows/workflows/1/start';
const options = {
  method: 'POST',
  headers: {Authorization: 'Api-Key  <apiKey>', 'Content-Type': 'application/json'},
  body: '{}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go Workflow that declares no inputs
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.simplified.com/api/v1/workflows/workflows/1/start"

	payload := strings.NewReader("{}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Api-Key  <apiKey>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby Workflow that declares no inputs
require 'uri'
require 'net/http'

url = URI("https://api.simplified.com/api/v1/workflows/workflows/1/start")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Api-Key  <apiKey>'
request["Content-Type"] = 'application/json'
request.body = "{}"

response = http.request(request)
puts response.read_body
```

```java Workflow that declares no inputs
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.simplified.com/api/v1/workflows/workflows/1/start")
  .header("Authorization", "Api-Key  <apiKey>")
  .header("Content-Type", "application/json")
  .body("{}")
  .asString();
```

```php Workflow that declares no inputs
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.simplified.com/api/v1/workflows/workflows/1/start', [
  'body' => '{}',
  'headers' => [
    'Authorization' => 'Api-Key  <apiKey>',
    'Content-Type' => 'application/json',
  ],
]);

echo $response->getBody();
```

```csharp Workflow that declares no inputs
using RestSharp;

var client = new RestClient("https://api.simplified.com/api/v1/workflows/workflows/1/start");
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Api-Key  <apiKey>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift Workflow that declares no inputs
import Foundation

let headers = [
  "Authorization": "Api-Key  <apiKey>",
  "Content-Type": "application/json"
]
let parameters = [] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api.simplified.com/api/v1/workflows/workflows/1/start")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```