> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://www.comet.com/docs/opik/reference/rest-api/spans/create-span/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://www.comet.com/_mcp/server.

# Create span

POST http://localhost:5173/api/v1/private/spans
Content-Type: application/json

Create span

Reference: https://www.comet.com/docs/opik/reference/rest-api/spans/create-span

## Servers

- `http://localhost:5173/api` (Local server, default)
- `https://www.comet.com/opik/api` (Opik Cloud)

## Request

### Body (application/json)

This endpoint expects a Span_Write.

- `start_time` (datetime, required)
- `id` (string, optional)
- `project_name` (string, optional) — If null, the default project is used
- `trace_id` (string, optional)
- `parent_span_id` (string, optional)
- `name` (string, optional)
- `type` (enum, optional)
  - Allowed values: `general`, `tool`, `llm`, `guardrail`
- `end_time` (datetime, optional)
- `input` (JsonListString_Write, optional)
- `output` (JsonListString_Write, optional)
- `metadata` (JsonListString_Write, optional)
- `model` (string, optional)
- `provider` (string, optional)
- `tags` (list of string, optional)
- `usage` (map from string to integer, optional)
- `error_info` (ErrorInfo_Write, optional)
- `last_updated_at` (datetime, optional)
- `total_estimated_cost` (double, optional)
- `total_estimated_cost_version` (string, optional)
- `ttft` (double, optional) — Time to first token in milliseconds
- `source` (enum, optional)
  - Allowed values: `sdk`, `experiment`, `playground`, `optimization`, `evaluator`
- `environment` (string, optional)

## Response

### 201

Created

## Errors

### 409 Conflict Error

Conflict

- `code` (integer, optional)
- `message` (string, optional)
- `details` (string, optional)

## Types

### JsonListString_Write

### ErrorInfo_Write

- `exception_type` (string, required)
- `traceback` (string, required)
- `message` (string, optional)

## Examples

**Request**

```json
{
  "start_time": "2024-01-15T09:30:00Z"
}
```

**Response**

```json
{}
```

**SDK Code**

```python
import requests

url = "http://localhost:5173/api/v1/private/spans"

payload = { "start_time": "2024-01-15T09:30:00Z" }
headers = {"Content-Type": "application/json"}

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

print(response.json())
```

```javascript
const url = 'http://localhost:5173/api/v1/private/spans';
const options = {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: '{"start_time":"2024-01-15T09:30:00Z"}'
};

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

```go
package main

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

func main() {

	url := "http://localhost:5173/api/v1/private/spans"

	payload := strings.NewReader("{\n  \"start_time\": \"2024-01-15T09:30:00Z\"\n}")

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

	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
require 'uri'
require 'net/http'

url = URI("http://localhost:5173/api/v1/private/spans")

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

request = Net::HTTP::Post.new(url)
request["Content-Type"] = 'application/json'
request.body = "{\n  \"start_time\": \"2024-01-15T09:30:00Z\"\n}"

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

```java
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("http://localhost:5173/api/v1/private/spans")
  .header("Content-Type", "application/json")
  .body("{\n  \"start_time\": \"2024-01-15T09:30:00Z\"\n}")
  .asString();
```

```php
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'http://localhost:5173/api/v1/private/spans', [
  'body' => '{
  "start_time": "2024-01-15T09:30:00Z"
}',
  'headers' => [
    'Content-Type' => 'application/json',
  ],
]);

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

```csharp
using RestSharp;

var client = new RestClient("http://localhost:5173/api/v1/private/spans");
var request = new RestRequest(Method.POST);
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"start_time\": \"2024-01-15T09:30:00Z\"\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift
import Foundation

let headers = ["Content-Type": "application/json"]
let parameters = ["start_time": "2024-01-15T09:30:00Z"] as [String : Any]

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

let request = NSMutableURLRequest(url: NSURL(string: "http://localhost:5173/api/v1/private/spans")! 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()
```

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