# Find the content type of a file name or an extension

`POST /v1/convert/string/extension/to/content_type`

Give a file name (backup.tar.gz resolves as a double extension, upper case is fine) or an extension with or without the dot. An unknown or missing extension is not an error: known is false so the flow can branch. The response says where the reference data comes from and when it was compiled.

## Request body

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| file_name | string | no | A file name such as report.PDF or backup.tar.gz |
| extension | string | no | An extension, with or without the dot |

## Example request

A request body that works, as JSON.

```json
{
  "extension": "xlsx"
}
```

## Code samples

Replace YOUR_TOKEN with your access token.

### curl

```shell
curl -X POST 'https://api.skillfulsardine.com/v1/convert/string/extension/to/content_type' \
  -H 'Authorization: Bearer YOUR_TOKEN' \
  -H 'Content-Type: application/json' \
  --data-raw '{
  "extension": "xlsx"
}'
```

### PowerShell

```powershell
$body = @'
{
  "extension": "xlsx"
}
'@
$response = Invoke-RestMethod -Method Post -Uri 'https://api.skillfulsardine.com/v1/convert/string/extension/to/content_type' `
  -Headers @{ Authorization = 'Bearer YOUR_TOKEN' } `
  -ContentType 'application/json; charset=utf-8' `
  -Body ([System.Text.Encoding]::UTF8.GetBytes($body))
$response | ConvertTo-Json -Depth 10
```

### Python

```python
import requests

payload = {
    "extension": "xlsx",
}

response = requests.post(
    "https://api.skillfulsardine.com/v1/convert/string/extension/to/content_type",
    headers={"Authorization": "Bearer YOUR_TOKEN"},
    json=payload,
    timeout=30,
)
print(response.json())
```

### JavaScript

```javascript
const response = await fetch("https://api.skillfulsardine.com/v1/convert/string/extension/to/content_type", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_TOKEN",
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "extension": "xlsx"
}),
});
const result = await response.json();
console.log(result);
```

### Node

```javascript
// Node 18 or later. Save as call.mjs and run: API_TOKEN=... node call.mjs
const token = process.env.API_TOKEN;

const response = await fetch("https://api.skillfulsardine.com/v1/convert/string/extension/to/content_type", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${token}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "extension": "xlsx"
}),
});
const result = await response.json();
console.log(result);
```

### Rust

```rust
// Cargo.toml: reqwest = { version = "0.12", features = ["blocking", "json"] }, serde_json = "1"
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let body: serde_json::Value = serde_json::from_str(r#"{
  "extension": "xlsx"
}"#)?;
    let response = reqwest::blocking::Client::new()
        .post("https://api.skillfulsardine.com/v1/convert/string/extension/to/content_type")
        .bearer_auth("YOUR_TOKEN")
        .json(&body)
        .send()?;
    println!("{}", response.text()?);
    Ok(())
}
```

### Swift

```swift
import Foundation

var request = URLRequest(url: URL(string: "https://api.skillfulsardine.com/v1/convert/string/extension/to/content_type")!)
request.httpMethod = "POST"
request.setValue("Bearer YOUR_TOKEN", forHTTPHeaderField: "Authorization")
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = Data(#"""
{
  "extension": "xlsx"
}
"""#.utf8)

let (data, _) = try await URLSession.shared.data(for: request)
print(String(decoding: data, as: UTF8.self))
```

## Response

The fields inside `data` of a successful response.

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| extension | string | yes | The extension used, lower case without a dot (tar.gz for double extensions) |
| content_type | string | yes | The content type, null when unknown |
| known | boolean | yes | False when the extension is missing or not in the reference data |
| data_source | string | yes | Where the reference data comes from |
| data_compiled | string | yes | When the reference data was compiled |

## Example response

A real answer from the operation, as JSON. The fields in the table above are inside `data`.

```json
{
  "data": {
    "extension": "xlsx",
    "content_type": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
    "known": true,
    "data_source": "Curated subset of the IANA media types registry (https://www.iana.org/assignments/media-types/) plus the de-facto types used by Microsoft 365 and common web tools",
    "data_compiled": "2026-10-16"
  },
  "errors": null,
  "meta": {
    "request_id": "b86cb6cb-6f20-4f6f-91df-f9a36d3dcdcb",
    "timestamp": "2026-10-27T07:19:42.031329Z",
    "version": "2026-03-26"
  },
  "pagination": null
}
```

## Responses

| Status | When it happens |
| --- | --- |
| 200 | Successful Response |
| 400 | The body respects the operation schema, but the use case rejected it. Each problem is one ApiError entry |
| 413 | The request is larger than the request size limit of the API allows |
| 422 | The body does not respect the operation schema. Each problem is one ApiError entry with the code validation_error |
| 500 | Something failed inside the server and was not an input problem. The same envelope, errors may be empty |

---
Source: https://skillfulsardine.com/developers/api/lookup-content-type/