open-distance

API

Response-compatible with Google's legacy Distance Matrix API, plus two extra arrays exposing per-endpoint geocode confidence.

Endpoint

GET https://open-distance.com/maps/api/distancematrix/json
    ?origins=<A>|<B>|...
    &destinations=<C>|<D>|...
    &units=imperial|metric        # default imperial
    &mode=driving                  # only mode supported

Each origin/destination is either an address string or a lat,lng pair. Multiple endpoints separated by |. Up to 100 elements (origins × destinations) per request.

Response

{
  "destination_addresses": ["…canonical or raw input…"],
  "destination_matches":   ["rooftop" | "interpolated" | "coords" | ""],
  "origin_addresses":      ["…"],
  "origin_matches":        ["…"],
  "rows": [
    { "elements": [
      { "status": "OK" | "NOT_FOUND" | "ZERO_RESULTS",
        "distance": { "text": "5.4 mi", "value": 8690 },
        "duration": { "text": "11 mins", "value": 660 } }
    ] }
  ],
  "status": "OK"
}

The confidence indicator

Each endpoint comes back with a match value telling you how it was located:

Value	Means	Typical accuracy
`rooftop`	Exact mapped point (NAD or OpenAddresses rooftop dataset)	Building-level
`interpolated`	OSM addr-tagged node, or TIGER segment interpolation	~30–100 m
`coords`	Caller-supplied `lat,lng` directly	Whatever the caller gave us
`""`	Geocode failed; raw input is echoed	Element returns `NOT_FOUND`

Caching

Successful responses send Cache-Control: public, max-age=3600, so Cloudflare's edge cache absorbs identical queries for an hour. The /coverage endpoint sends max-age=86400. You're welcome to cache responses in your own backend for as long as you like.

Rate limits

Per-IP rate limits on the hosted deployment:

25 requests per second
500 requests per hour
10,000 requests per day

There is no paid tier. The hosted instance is intentionally a free shared resource for casual use. If you need higher limits, self-host on your own Cloudflare account — limits are env-var configurable per tier, or set all three to 0 for an unlimited deployment.

Response headers

Every API response (both 200 success and 429 rate-limited) carries the following headers so you can self-throttle without a probe round-trip:

Header	What it means
`X-RateLimit-Limit-Second`	Configured per-second limit (25 by default)
`X-RateLimit-Remaining-Second`	Requests left in the current 1-second window
`X-RateLimit-Reset-Second`	Seconds until the 1-second window rolls (always 1)
`X-RateLimit-Limit-Hour`	Configured per-hour limit (500 by default)
`X-RateLimit-Remaining-Hour`	Requests left in the current hour bucket
`X-RateLimit-Reset-Hour`	Seconds until the hour bucket rolls
`X-RateLimit-Limit-Day`	Configured per-day limit (10,000 by default)
`X-RateLimit-Remaining-Day`	Requests left in the current day bucket
`X-RateLimit-Reset-Day`	Seconds until the day bucket rolls
`RateLimit-Limit`	IETF draft header: limit of the tightest tier
`RateLimit-Remaining`	Remaining of the tightest tier
`RateLimit-Reset`	Seconds until the tightest tier resets

When you hit the limit

You get HTTP 429 with "status":"OVER_QUERY_LIMIT", a Retry-After header (seconds until the offending tier rolls), and X-RateLimit-Tier = sec / hour / day indicating which bucket overflowed. The response body includes a link back to the source so you can self-host with your own limits.

Deviations from the legacy Distance Matrix shape

No fare, duration_in_traffic, geocoded_waypoints, copyrights, or warnings fields.
place_id: inputs return NOT_FOUND.
Only mode=driving is supported.
match arrays added (the legacy schema ignores unknown fields, so existing clients are unaffected).
Centroid-quality geocodes return NOT_FOUND rather than confidently-wrong distances.

Other endpoints

Path	What it returns
`/healthz`	Liveness + sentinel-tile probe
`/coverage`	Version, data sources, supported match values

Self-hosting

The whole stack (Cloudflare Worker + R2 + D1 + KV) costs ~$5–10/month for the entire continental US. Source: github.com/kurtpayne/open-distance. ./refresh.sh handles the data pipeline from a clean clone.