Taginfo always had an API so everybody can access all the juicy data in its database through simple HTTP queries. But that API was never used by anyone (as far as I can tell from a quick look at the log files). One reason was probably that I didn’t document the API.
I have done this now on the wiki. The API calls themselves are documented right inside Taginfo itself [UPDATE: URL], they are autogenerated from the code. The documentation is not perfect, but its a start. I have documented the API calls I consider more stable, some others are still undocumented.
I have also added a small sample program accessing this API.