For API developers building paid Lightning services

L402 Launch Checker | Maximum Sats

L402 Launch Checker

Check any API endpoint for Lightning Network 402 support in seconds. No setup, no code changes, no commitments.

Common Use Cases

Podcast feeds — gate access to episodes with Lightning payments
API paywalls — meter usage and charge per request with sats
Content APIs — monetize data feeds and digital assets
Microservices — add payment auth to internal service calls

Built for the L402 Ecosystem

Launch Checker is built by the team behind Alby and the L402 protocol spec. The same tooling used to validate L402 implementations is now available for anyone.

Used by developers integrating Lightning payments into production APIs — from indie podcasters to infrastructure teams.

What It Does

The L402 Launch Checker probes your API endpoint and tells you whether it is ready to accept Lightning payments via the L402 protocol. It runs a series of automated checks:

Reachability - Can the endpoint be contacted?
Method Support - Does it accept GET or POST?
Challenge Detection - Does it respond with L402-style authentication challenges?
Content Signals - Does the response contain L402 invoice or payment fields?

Run a preflight check in under 5 seconds. Run a full scan after payment to get a detailed report with actionable fixes.

How It Works

1. Enter Your Endpoint

Provide the URL of the API endpoint you want to check and the HTTP method you use to call it.

2. Run a Preflight Check

Our lightweight probe sends a single request to your endpoint and analyzes the response for L402 signals. You will get an immediate classification:

Supported - Your endpoint shows clear L402 behavior
Unsupported - No L402 signals detected
Unclear - The probe could not confirm either way

3. Run a Full Scan (After Payment)

A full scan executes the complete L402 flow against your endpoint:

Detects the exact challenge response format
Parses the invoice from the 402 response
Verifies payment hash consistency
Captures a full transcript of the exchange
Generates a prioritized fix list if something is not working

What You Get

	Preflight	Full Scan
Reachability check	Yes	Yes
Method validation	Yes	Yes
Challenge detection	Yes	Yes
Invoice parsing	-	Yes
Payment verification	-	Yes
Transcript capture	-	Yes
Fix recommendations	-	Yes

When to Run the Paid Scan

Run the full scan when you want a complete diagnostic — not just a yes/no signal. The paid scan:

Detects the exact format of the L402 challenge your endpoint returns
Parses the invoice and verifies the payment hash consistency
Captures a full transcript of the L402 exchange
Generates a prioritized fix list ranked by impact

If the preflight says "unsupported" or "unclear," the paid scan tells you exactly why and what to change.

Pricing

Preflight check: Free
Full scan: 49 sats per scan

Launch pricing: Full scan is 49 sats — below cost to validate demand.

Full scan: 49 sats per scan

Scans are capped. You set the maximum spend before running. If the scan exhausts your cap, you pay only what was actually spent.

FAQ

What if my endpoint is not L402-ready yet?: That is the most common outcome and exactly when the paid scan is most useful. It tells you exactly what is missing and how to fix it.
How is this different from reading the L402 spec?: The spec describes what L402 should do. The scan tells you what your implementation actually does and where it diverges.
How long does the scan take?: Usually under 10 seconds. You set a max spend cap so costs are controlled.
What does the paid scan give me that the free preflight does not?: Extended challenge-response testing, invoice parsing and verification, full transcript capture, and a prioritized fix list with exact guidance.

Run a Preflight Check

View a sample report