# Find out what a file really is

`POST /v1/check/file/type`

Reads the file content (base64, as a flow already has it) and reports the type found in the bytes: PDF, Word, Excel and PowerPoint (told apart inside the zip), ZIP, PNG, JPEG, GIF and more, or JSON, XML, CSV and plain text. Also reports the size, whether the file is empty, and whether the file name agrees. A mismatch is reported, never corrected. An unrecognised file is not an error: the type is null.

## Request body

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| content_base64 | string | yes | The file content as base64. File content in a flow is already base64: send it as it is |
| file_name | string | no | The name the file has, to compare with the content |

## Example request

A request body that works, as JSON.

```json
{
  "content_base64": "YSxiCjEsMg==",
  "file_name": "invoices.csv"
}
```

## Code samples

Replace YOUR_TOKEN with your access token.

### curl

```shell
curl -X POST 'https://api.skillfulsardine.com/v1/check/file/type' \
  -H 'Authorization: Bearer YOUR_TOKEN' \
  -H 'Content-Type: application/json' \
  --data-raw '{
  "content_base64": "YSxiCjEsMg==",
  "file_name": "invoices.csv"
}'
```

### PowerShell

```powershell
$body = @'
{
  "content_base64": "YSxiCjEsMg==",
  "file_name": "invoices.csv"
}
'@
$response = Invoke-RestMethod -Method Post -Uri 'https://api.skillfulsardine.com/v1/check/file/type' `
  -Headers @{ Authorization = 'Bearer YOUR_TOKEN' } `
  -ContentType 'application/json; charset=utf-8' `
  -Body ([System.Text.Encoding]::UTF8.GetBytes($body))
$response | ConvertTo-Json -Depth 10
```

### Python

```python
import requests

payload = {
    "content_base64": "YSxiCjEsMg==",
    "file_name": "invoices.csv",
}

response = requests.post(
    "https://api.skillfulsardine.com/v1/check/file/type",
    headers={"Authorization": "Bearer YOUR_TOKEN"},
    json=payload,
    timeout=30,
)
print(response.json())
```

### JavaScript

```javascript
const response = await fetch("https://api.skillfulsardine.com/v1/check/file/type", {
  method: "POST",
  headers: {
    "Authorization": "Bearer YOUR_TOKEN",
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "content_base64": "YSxiCjEsMg==",
  "file_name": "invoices.csv"
}),
});
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/check/file/type", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${token}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
  "content_base64": "YSxiCjEsMg==",
  "file_name": "invoices.csv"
}),
});
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#"{
  "content_base64": "YSxiCjEsMg==",
  "file_name": "invoices.csv"
}"#)?;
    let response = reqwest::blocking::Client::new()
        .post("https://api.skillfulsardine.com/v1/check/file/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/check/file/type")!)
request.httpMethod = "POST"
request.setValue("Bearer YOUR_TOKEN", forHTTPHeaderField: "Authorization")
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = Data(#"""
{
  "content_base64": "YSxiCjEsMg==",
  "file_name": "invoices.csv"
}
"""#.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 |
| --- | --- | --- | --- |
| content_type | string | yes | Detected from the content, null when not recognised |
| extension | string | yes | The usual extension of that type |
| size_bytes | integer | yes | Size of the content |
| is_empty | boolean | yes | True for zero bytes, or text that is only blank space |
| name_extension | string | yes | The extension of file_name |
| name_content_type | string | yes | The content type file_name suggests |
| name_matches | boolean | yes | Whether the name agrees with the content. Null without a file name, or when the name's extension is unknown |
| mismatch_reason | string | yes | What disagrees, when name_matches is false |

## Example response

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

```json
{
  "data": {
    "content_type": "text/csv",
    "extension": "csv",
    "size_bytes": 7,
    "is_empty": false,
    "name_extension": "csv",
    "name_content_type": "text/csv",
    "name_matches": true,
    "mismatch_reason": null
  },
  "errors": null,
  "meta": {
    "request_id": "b77887d7-483e-4327-b4a8-d17cdf1bc321",
    "timestamp": "2026-10-27T07:19:42.136864Z",
    "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/detect-file-type/