The author of this tool shared it's first release in a (2018) blog post:

Tooling for Invoices in Lightning Network Applications https://medium.com/lightwork/development-tooling-for-invoices-in-lightning-network-applications-cf3d194dc2bb

See also:

bolt11 invoice interactive explorer #68012 https://www.bolt11.org

Here's an example of where LightningDecoder came in very handy:

How to prove that a LN invoice was paid when using Wallet of Satoshi? #212420