Developer API Reference

Automate branded short link creation using our simple HTTP REST API. Perfect for product integrations, campaigns, and dashboards.

Authentication

Authenticate your requests by passing your generated API key in the headers. You can generate API credentials directly inside the API Keys Dashboard.

Supported Authorization Headers

AuthorizationBearer ul0_yourApiKeyHere

X-API-Keyul0_yourApiKeyHere

Shorten URL

POSThttps://ul0.site/api/shorten

Submit a payload containing the target URL. If a connected custom domain is specified, we check ownership, register the record in your account, and create a short URL targeting your custom link.

Parameter	Type	Required	Description
longUrl	string	Yes	The full destination web address to redirect readers to.
host	string	No	Connected custom domain (e.g., `link.yourbrand.com`). Defaults to `ul0.site`.
customSlug	string	No	Desirable slug identifier (path component). Auto-generated if omitted.

Request Integration Samples

curl -X POST https://ul0.site/api/shorten \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "longUrl": "https://example.com/very-long-product-details-link",
    "host": "link.yourbrand.com",
    "customSlug": "summer-promo"
  }'

Rate Limits

Programmatic requests carry different rate limits depending on your subscribed account tier:

Pro Plan Keys

Allows up to **60 requests per minute** per key. Ideal for small applications.

Business Plan Keys

Allows up to **300 requests per minute** per key. Perfect for scaling enterprise systems.

Error Responses

The API will return appropriate HTTP response status codes along with descriptive JSON error objects if a call fails:

401 Unauthorized

Occurs if the API key header is missing or incorrect.

403 Forbidden

Occurs if attempting to shorten on a custom domain (`host`) that is not connected or verified on your account.

409 Conflict

Occurs if the requested `customSlug` is already taken on that domain.

429 Too Many Requests

Occurs if you exceed the minute rate limit associated with your active plan.