> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://api.docs.modulards.com/modular-ds-public-api/oauth/client-registration/register-an-mcp-client/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://api.docs.modulards.com/_mcp/server.

# Register an MCP client

POST https://api.modulards.com/oauth/register
Content-Type: application/json

Registers a public OAuth client (RFC 7591) so an MCP client can start the authorization flow. Use it once per client installation, then keep the returned `client_id`.

The client is public: it uses the authorization code flow with PKCE (`S256`) and no client secret. Any other RFC 7591 metadata you send is ignored. Registrations that never obtain a token are removed after 30 days.

Public and throttled to 10 requests per minute per IP address; the eleventh answers 429. Served at the root of the MCP host, without the `/api` prefix.

**Body**
- `redirect_uris` (array of strings, required): 1 to 5 addresses the authorization code may be sent to. Each one must be one of these:
  - An `https` address on any host. The approval screen shows the user the origin the code will be sent to.
  - An `http` address on a loopback host (`127.0.0.1`, `[::1]` or `localhost`), on any port, for native and desktop clients (RFC 8252). `http` on any other host is refused.
  - A private-use scheme with a host, which native clients use for their callback (RFC 8252), such as `cursor://anysphere.cursor-retrieval/oauth/callback`. Any scheme is accepted except those a browser runs, reads from disk or keeps for itself (for example `javascript`, `data`, `file`, `ftp`, `ws`, `chrome-extension`).

  Whatever the origin or scheme, an address with a comma, `@`, backslash, whitespace, control character, user name, password or fragment is refused, and so is a host that Modular DS has blocked (with its subdomains). A refused address answers `400` with `invalid_redirect_uri`.
- `client_name` (string, optional): the name the approval screen shows to the user, at most 100 characters and no control characters. It is shown next to the address the authorization will be sent to.

**Errors**
- **400**: a redirect URI is missing, more than five are sent or one is not accepted (`invalid_redirect_uri`).
- **400**: `client_name` is too long or contains control characters (`invalid_client_metadata`).

Reference: https://api.docs.modulards.com/modular-ds-public-api/oauth/client-registration/register-an-mcp-client

## Request

### Body (application/json)

This endpoint expects an object.

- `client_name` (string, optional)
- `redirect_uris` (list of string, optional)

## Response

### 201

201 Created

- `client_id` (string, optional) — Identifier of the new client; keep it to start the authorization flow.
- `grant_types` (list of enum, optional) — Grant types the client may use: `authorization_code` and `refresh_token`.
  - Allowed values: `authorization_code`, `refresh_token`
- `redirect_uris` (list of string, optional) — The redirect addresses that were registered.
- `response_types` (list of enum, optional) — Response types the client may use; always `code`.
  - Allowed values: `code`
- `scope` (string, optional) — Scope granted to the client: `mcp:use`.
- `token_endpoint_auth_method` (enum, optional) — How the client authenticates at the token endpoint; always `none`, because the client is public.
  - Allowed values: `none`

## Errors

### 400 Bad Request Error

400 Invalid redirect URI

- `error` (enum, optional) — `invalid_redirect_uri` when a redirect address is refused, `invalid_client_metadata` for any other invalid field.
  - Allowed values: `invalid_redirect_uri`, `invalid_client_metadata`
- `error_description` (string, optional) — Sentence saying which field was refused.

## Examples

### 201 Created

**Response**

```json
{
  "client_id": "9d7f2c1e-4b3a-4f8e-9c2d-1a5b6e7f8a90",
  "grant_types": [
    "authorization_code",
    "refresh_token"
  ],
  "redirect_uris": [
    "https://claude.ai/api/mcp/auth_callback"
  ],
  "response_types": [
    "code"
  ],
  "scope": "mcp:use",
  "token_endpoint_auth_method": "none"
}
```

**SDK Code**

```python 201 Created
import requests

url = "https://api.modulards.com/oauth/register"

response = requests.post(url)

print(response.json())
```

```javascript 201 Created
const url = 'https://api.modulards.com/oauth/register';
const options = {method: 'POST'};

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

```go 201 Created
package main

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

func main() {

	url := "https://api.modulards.com/oauth/register"

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

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

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

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

}
```

```ruby 201 Created
require 'uri'
require 'net/http'

url = URI("https://api.modulards.com/oauth/register")

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

request = Net::HTTP::Post.new(url)

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

```java 201 Created
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.modulards.com/oauth/register")
  .asString();
```

```php 201 Created
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.modulards.com/oauth/register');

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

```csharp 201 Created
using RestSharp;

var client = new RestClient("https://api.modulards.com/oauth/register");
var request = new RestRequest(Method.POST);
IRestResponse response = client.Execute(request);
```

```swift 201 Created
import Foundation

let request = NSMutableURLRequest(url: NSURL(string: "https://api.modulards.com/oauth/register")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"

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()
```

### Register an MCP client

**Request**

```json
{
  "client_name": "My MCP client",
  "redirect_uris": [
    "http://example.com/callback"
  ]
}
```

**Response**

```json
{
  "client_id": "9d7f2c1e-4b3a-4f8e-9c2d-1a5b6e7f8a90",
  "grant_types": [
    "authorization_code",
    "refresh_token"
  ],
  "redirect_uris": [
    "https://claude.ai/api/mcp/auth_callback"
  ],
  "response_types": [
    "code"
  ],
  "scope": "mcp:use",
  "token_endpoint_auth_method": "none"
}
```

**SDK Code**

```python Register an MCP client
import requests

url = "https://api.modulards.com/oauth/register"

payload = {
    "client_name": "My MCP client",
    "redirect_uris": ["http://example.com/callback"]
}
headers = {"Content-Type": "application/json"}

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

print(response.json())
```

```javascript Register an MCP client
const url = 'https://api.modulards.com/oauth/register';
const options = {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: '{"client_name":"My MCP client","redirect_uris":["http://example.com/callback"]}'
};

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

```go Register an MCP client
package main

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

func main() {

	url := "https://api.modulards.com/oauth/register"

	payload := strings.NewReader("{\n  \"client_name\": \"My MCP client\",\n  \"redirect_uris\": [\n    \"http://example.com/callback\"\n  ]\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 Register an MCP client
require 'uri'
require 'net/http'

url = URI("https://api.modulards.com/oauth/register")

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

request = Net::HTTP::Post.new(url)
request["Content-Type"] = 'application/json'
request.body = "{\n  \"client_name\": \"My MCP client\",\n  \"redirect_uris\": [\n    \"http://example.com/callback\"\n  ]\n}"

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

```java Register an MCP client
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.modulards.com/oauth/register")
  .header("Content-Type", "application/json")
  .body("{\n  \"client_name\": \"My MCP client\",\n  \"redirect_uris\": [\n    \"http://example.com/callback\"\n  ]\n}")
  .asString();
```

```php Register an MCP client
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.modulards.com/oauth/register', [
  'body' => '{
  "client_name": "My MCP client",
  "redirect_uris": [
    "http://example.com/callback"
  ]
}',
  'headers' => [
    'Content-Type' => 'application/json',
  ],
]);

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

```csharp Register an MCP client
using RestSharp;

var client = new RestClient("https://api.modulards.com/oauth/register");
var request = new RestRequest(Method.POST);
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"client_name\": \"My MCP client\",\n  \"redirect_uris\": [\n    \"http://example.com/callback\"\n  ]\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift Register an MCP client
import Foundation

let headers = ["Content-Type": "application/json"]
let parameters = [
  "client_name": "My MCP client",
  "redirect_uris": ["http://example.com/callback"]
] as [String : Any]

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

let request = NSMutableURLRequest(url: NSURL(string: "https://api.modulards.com/oauth/register")! 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()
```