Add basic API doc.

doc/README.md

@@ -19,6 +19,7 @@
 - [Code Contribution Guidelines](developer/Code-Contribution-Guidelines.md)
 - [Developer Machine Setup](developer/Setup.md)
 - [Mattermost Style Guide](developer/Style-Guide.md)
+- [API Overview] (api/Overview.md)
 
 ## Usage Help
 

doc/api/README.md

@@ -0,0 +1,94 @@
+# API Overview
+
+This provides a basic overview of the Mattermost API. All examples assume there is a Mattermost instance running at http://localhost:8065.
+
+## Schema
+
+All API access is done through `yourdomain.com/api/v1/`, with all data being sent and received as JSON.
+
+
+## Authentication
+
+The majority of the Mattermost API involves interacting with teams. Therefore, most API methods require authentication as a user. There are two ways to authenticate into a Mattermost system.
+
+##### Session Token
+
+Make an HTTP POST to `yourdomain.com/api/v1/users/login` with a JSON body indicating the `name` of the team, the user's `email` and `password`.
+
+```
+curl -i -d '{"name":"exampleteam","email":"someone@nowhere.com","password":"thisisabadpassword"}' http://localhost:8065/api/v1/users/login
+```
+
+If successful, the response will contain a `Token` header and a User object in the body.
+
+```
+HTTP/1.1 200 OK
+Set-Cookie: MMSID=hyr5dmb1mbb49c44qmx4whniso; Path=/; Max-Age=2592000; HttpOnly
+Token: hyr5dmb1mbb49c44qmx4whniso
+X-Ratelimit-Limit: 10
+X-Ratelimit-Remaining: 9
+X-Ratelimit-Reset: 1
+X-Request-Id: smda55ckcfy89b6tia58shk5fh
+X-Version-Id: developer
+Date: Fri, 11 Sep 2015 13:21:14 GMT
+Content-Length: 657
+Content-Type: application/json; charset=utf-8
+
+{{user object as json}}
+```
+
+Include the `Token` as part of the `Authentication` header on your future API requests with the `Bearer` method.
+
+```
+curl -i -H 'Authorization: Bearer hyr5dmb1mbb49c44qmx4whniso' http://localhost:8065/api/v1/users/me
+```
+
+That's it! You should now be able to access the API as the user you logged in as.
+
+##### OAuth2
+
+Coming soon...
+
+
+## Client Errors
+
+All errors will return an appropriate HTTP response code along with the following JSON body:
+
+```
+{
+    "message": "", // the reason for the error
+    "detailed_error": "", // some extra details about the error
+    "request_id": "", // the ID of the request
+    "status_code": 0 // the HTTP status code
+}
+```
+
+
+## Rate Limiting
+
+Whenever you make an HTTP request to the Mattermost API you might notice the following headers included in the response:
+```
+X-Ratelimit-Limit: 10
+X-Ratelimit-Remaining: 9
+X-Ratelimit-Reset: 1441983590
+
+```
+
+These headers are telling you your current rate limit status.
+
+Header                | Description
+--------------------- | -----------
+X-Ratelimit-Limit     | The maximum number of requests you can make per second.
+X-Ratelimit-Remaining | The number of requests remaining in the current window.
+X-Ratelimit-Reset     | The remaining UTC epoch seconds before the rate limit resets.
+
+If you exceed your rate limit for a window you will receive the following error in the body of the response:
+```
+HTTP/1.1 429 Too Many Requests
+Date: Tue, 10 Sep 2015 11:20:28 GMT
+X-RateLimit-Limit: 10
+X-RateLimit-Remaining: 0
+X-RateLimit-Reset: 1
+
+limit exceeded
+```