Authentication

Network reference: For the full authentication guide covering all Tools.FAST sites, see tools.fast/api/docs/authentication.

API key header

Pass your API key in the X-Fast-Api-Key header:

X-Fast-Api-Key: fast_prod_...

All endpoints require X-Fast-Api-Key.

Server-side only

The API is designed for server-side integrations. Browser-based requests are restricted to first-party origins — call the API from your backend. Cross-origin requests from third-party domains will be blocked by CORS policy.

Getting your API key

1. Create a free account (500 Pro credits, no card required).
2. Navigate to API Keys.
3. Create a new key — it will start with fast_prod_.
4. Store the key securely; it is shown only once.

Key management

You can create multiple API keys — for example, separate keys for staging and production, or per-application. Revoke any key individually from the API Keys page. Revoked keys stop working immediately.

IP allowlisting

When creating an API key, you can restrict it to specific IP addresses. Enter a single address (e.g., 203.0.113.5) or a CIDR range (e.g., 203.0.113.0/24). Requests from non-allowlisted IPs will be rejected with a 401.

We recommend allowlisting your server IPs in production — it limits the blast radius if a key is ever leaked.

Example error

{
  "error": "api_key.invalid_or_ip_not_allowed",
  "detail": "X-Fast-Api-Key was provided but is invalid for this request (or IP not allowlisted)."
}

Example usage

# Action endpoint (requires API key)
curl -sS -X POST "https://api.tools.fast/convert" \
  -H "X-Fast-Api-Key: fast_prod_your_key_here" \
  -F "file=@photo.heic" \
  -F "targetFormat=jpg"

# Discovery endpoint
curl -sS "https://api.tools.fast/convert/conversions" \
  -H "X-Fast-Api-Key: fast_prod_your_key_here"

# Action endpoint (requires API key)
Invoke-RestMethod -Method Post "https://api.tools.fast/convert" `
  -Headers @{ "X-Fast-Api-Key" = "fast_prod_your_key_here" } `
  -Form @{ file = Get-Item "photo.heic"; targetFormat = "jpg" }

# Discovery endpoint
Invoke-RestMethod "https://api.tools.fast/convert/conversions" `
  -Headers @{ "X-Fast-Api-Key" = "fast_prod_your_key_here" }