SF Muni Agent [aka Darby learns how to code a basic agent]

Powered by Claude that gives you real-time SF Muni arrival predictions. Ask it about any stop and it'll tell you what's coming and when.

Note: 511 has a very low rate limit of 60 req/hour. You will hit it if you spam the chat. Also, this agent is not very good at non-station locations and transfers. It's pretty basic.

$ go run .
Chat with Claude (use 'ctrl-c' to quit)
You: what's coming to church station?
tool: get_muni_arrivals({"location":"Church Station"})
Claude: Here are the available directions at Church Station:

  Outbound (OB) - Lines K, L, M
  Toward: 47th Ave & Cutler Ave, Balboa Park BART, San Jose Ave & Niagara Ave

  Inbound (IB) - Lines K, L, M
  Toward: Metro Embarcadero Station (downtown)

Which direction are you heading?
You: outbound
tool: get_muni_arrivals({"location":"Church Station","direction":"OB"})
Claude: Here are the next Outbound departures from Church Station:

  [K] INGLESIDE → Balboa Park BART — 4 min
  [M] OCEAN VIEW → San Jose Ave & Niagara Ave — 6 min
  [L] TARAVAL → 47th Ave & Cutler Ave — 8 min
  [K] INGLESIDE → Balboa Park BART — 14 min
  [M] OCEAN VIEW → San Jose Ave & Niagara Ave — 17 min

It accounts for your travel time to the station too:

You: im 30 min walk from church station and i want to go to embarcadero. what train should i take?
tool: get_muni_arrivals({"location":"Church Station"})
tool: get_muni_arrivals({"location":"Church Station","direction":"IB"})
Claude: Take **K, L, or M** inbound - all go directly to Embarcadero.

Since you're 30 min away, catch one of these:
• **K** - 39 min from now
• **L** - 43 min from now
• **M** - 45 min from now

All are direct - no transfers needed.

Setup

1. Get an Anthropic API key and a 511.org API key.

2. Set environment variables:

   export ANTHROPIC_API_KEY="your-key"
   export MUNI_API_KEY="your-511-key"

3. Run it:

   go run .

How it works

The agent skeleton (chat loop, tool dispatch, inference) comes from Thorsten Ball's tutorial How to Build an Agent. On top of that, a get_muni_arrivals tool provides real-time transit data via the 511.org API:

• Stop lookup — searches all SF Muni stops by name, or geocodes a street address and finds the nearest stop.
• Direction filtering — called without a direction, it returns the available directions (IB/OB) and their lines. Called with a direction, it returns upcoming departures. Infers direction from context when possible.
• Travel time aware — if you mention how far you are from the station, it filters out trains you can't catch.
• Real-time data — uses the SIRI StopMonitoring endpoint for live predictions, marked with a LIVE indicator when GPS-based.

Project structure

File	Purpose
main.go	Agent loop, tool dispatch, Claude API calls
muni.go	Muni tool: stop search, geocoding, 511 API integration