L402 is a protocol for machine-to-machine payments. It allows agents to go out and purchase resources or access tokens to APIs online. If this sounds familiar, you might have heard of it before or of other similar protocols such as X402 or MPP (the Machine Payments Protocol). But in this post, we're talking about L402.

A Quick History Lesson

The HTTP error code 402, "Payment Required," was originally created back in the mid-90s and held for future use. Then, years later in 2020, Lightning Labs created the L402 protocol. This was originally called LSAT, or Lightning Service Authentication Token, and this protocol made use of this long-dormant HTTP error code.

Personally, I think how this works is quite beautiful.…