Here's a summary of the discussion (RAML vs Swagger vs Apiary vs RSpec...) we had at Lonely Planet: https://lonelyplanet.atlassian.net/wiki/display/PUB/API+Spec...

5 months in, we're happy with API Blueprint. We used to use Dredd for API validation but ran into to some limitations:

- Dredd does not perform any validation against the siren response beyond the first key level. For example, it does not validate if the class-name is user-events, or usr-events

- Dredd does not make any difference between Action parameters and Resource parameters. Then, an action POST to create user-events will have undesired url parameters. E.G: POST /user-events?take=0&skip=2 (The apib blueprint specs allows to make this difference: https://github.com/apiaryio/api-blueprint/blob/master/exampl...)

So one of our devs created a Ruby validator, https://github.com/nogates/vigia. See http://engineering.lonelyplanet.com/2014/11/18/vigia-integra... if you're interested.