[dasmoth]

Possibly depends what you mean by "API", but I really like the SQLite documentation with its graphical representations of the query syntax.

[joezydeco]

Backus-Naur diagrams are sweet. I used to covet the one that Apple put out for Apple Pascal:

https://www.bytecellar.com/2004/06/15/apples_pascal_s/

[Jugurtha]

I believe these are called "railroad diagrams". BNF is text only as far as I know.

There are BNF to railroad diagram generators (they take a "grammar file", often BNF, and output a railroad diagram).

[dasmoth]

Oh, that poster is nice!

And thanks for giving me a name for them, too.

[joezydeco]

In my mind I picture Steve Jobs dropping a little acid and staring at this poster for a few hours...

[archagon]

The SQLite docs were frequently better than blog posts or SO questions about my issues, which was a first for me.