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This guide walks you through creating a sandbox account, generating an API key, and verifying that you can connect to the Circle Mint API.

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Prerequisites

Before you begin, ensure you have:
  • A valid email address to register for a Circle Mint sandbox account
  • curl or another tool for making HTTP requests

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Step 1: Create a sandbox account

The sandbox environment lets you test API integrations without processing real transactions. For more details on sandbox versus production environments, see Sandbox to Production.
1

Sign up for a sandbox account

Go to app-sandbox.circle.com/signup and complete the registration form.
2

Verify your email address

Check your inbox and confirm your email to activate your account.
3

Log in to the sandbox

After activation, log in at https://app-sandbox.circle.com.

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Step 2: Generate an API key

Circle Mint uses API keys to authenticate all requests. Create and manage keys in the Mint Console.
1

Open the Mint Console

Go to app-sandbox.circle.com/developer.
2

Select the API Keys tab

3

Click Create an API key

4

Enter a name for your key

5

(Optional) Add IP addresses to the allowlist

Restrict where the key can be used from.
6

Click Create API key

7

Copy the key and store it securely

API keys grant access to privileged operations on Circle APIs. Store your API key securely and never expose it in client-side code, public repositories, or other publicly accessible locations. All API requests must be made over HTTPS. You can create a maximum of 10 API keys per environment.
You can also harden API access with a transport-layer certificate check.
You can add mutual TLS (mTLS) on top of API key authentication for an extra layer of transport-level security. Opting in is optional for most customers and required for entities operating under the EU Markets in Crypto-Assets (MiCA) regulation. mTLS changes how you generate and rotate API keys. See How mTLS authentication works.

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Step 3: Test connectivity

Test raw connectivity by calling the /ping endpoint. This endpoint does not require authentication, so it confirms that your application can reach the API. 
curl -s https://api-sandbox.circle.com/ping
If your application reached the API, you see the following response: 
{ "message": "pong" }

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Step 4: Verify your API key

Circle Mint uses Bearer token authentication. Include your API key in the Authorization header of every request using the format Bearer YOUR_API_KEY. Call the /v1/configuration endpoint to confirm that your API key is valid and properly configured: 
curl -s https://api-sandbox.circle.com/v1/configuration \
  -H "Authorization: Bearer ${YOUR_API_KEY}"
A successful response returns your account configuration, including your masterWalletId. The masterWalletId is the identifier for the primary wallet associated with your Circle Mint account, used as the source or destination in transfer and payout operations. 
{ "data": { "payments": { "masterWalletId": "1234567890" } } }
If the API key is missing or malformed, you receive a 401 Unauthorized error: 
{
  "code": 401,
  "message": "Malformed authorization. Are the credentials properly encoded?"
}
If you see this error, verify that your Authorization header uses the Bearer prefix and that you copied the full API key from the Mint Console.

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Use the TypeScript SDK (optional)

Circle publishes a TypeScript SDK that wraps the Circle Mint API. Install it from the npm registry: 
npm install @circle-fin/circle-sdk
See the circle-nodejs-sdk repository for usage examples, type definitions, and instructions for filing issues or contributing.