511.org/transit/StopMonitoring is a very useful API for getting real-time transit arrival data for transit systems in the SF Bay Area. Unfortunately, it offers little in the way of filtering that data down. You can either provide a stopcode URL param and get arrivals for one single stop, or you can omit the param and get arrivals for every stop in the system. This adds up to anywhere between 5MB and 30MB of JSON for SFMTA depending on the time of day. With a normal computer this isn't a big deal, but when working with small embedded systems it's unusably large. Requesting multiple individual stops is also a non-starter due to the 60 request per hour rate limit on the endpoint.
511-proxy is a simple Express app that works as a proxy to the StopMonitoring endpoint and accepts most of the same URL parameters. However, it filters the arrivals down with a more useful set of params.
This app is running live on my personal server. Simply obtain a 511.org API key and hit 511proxy.wn.zone:
https://511proxy.wn.zone/transit/StopMonitoring?api_key=your-api-key&agency=SF&stopcodes=12345|67890&line_ids=5R|N|38&directions=IB|OB|N|S|W|E
This returns the same API response format as the normal StopMonitoring endpoint, but with the MonitoredStopVisit array cut down to only the specified stop codes, lines, and directions specified in the URL. You may omit some or all of the filter params as you see fit.
Additionally, the hosted version of this API supports both https and http for embedded applications, and does not gzip/brotli encode anything.
Don't trust me with your 511 API key? Run it yourself.
npm i
npm run build
npm run start
OR
docker run -p 42424:42424 karmeleon/511-proxy