API fair-use rate limiting

Fair-use limiting is the etiquette layer on a keyless public API: rather than charging for calls, the operator publishes behavioural rules and enforces them at the network edge.

USGS Water Services is the catalog's worked example. Its terms ask users to scope queries efficiently - "No one user is allowed to download all of the data with a single call" - support gzip responses, and block IPs "returning HTTP 403 Access_Forbidden for excessive use", with an unblock request form available for recovery.

Behind the rules sits a large service: Instantaneous Values readings at 5-60 minute intervals from October 2007 onward, daily values back over a century (a verified record from 1931 for site 01646500), across roughly 1.5 million monitored sites.

Keyless APIs tempt teams into full-universe pulls, and fair-use rules turn that instinct into an outage.

• The forbidden query is the obvious one. 'Download everything' is explicitly disallowed - architectures that enumerate all sites and parameters will trip the 403 long before they finish.

• Blocks are IP-level and manual to reverse. An Access_Forbidden block takes an unblock request to lift, so one careless job can silence a shared office IP or CI runner.

• Provisional status overlays freshness. Real-time readings carry the provisional-data disclaimer and must not inform legal or regulatory decisions until approved - freshness and authority are separate properties here.

• Free does not mean unmetered. No key and no charge still leaves a fairness contract; vendors reselling USGS data inherit the same constraints.

1. Look for the written rule, not folklore. USGS publishes its expectation verbatim - efficient scoping, no wholesale download - and a source without stated limits may enforce them anyway.
2. Design around spatial filters. State, county, HUC watershed code and bounding-box filters exist precisely to keep queries scoped; use them in every job.
3. Enable compression and lean formats. Gzip support and tab-delimited RDB output reduce bytes per call, which is half the fairness equation.

These entries cover the services the fair-use rules govern: - instantaneous values service — USGS's real-time feed of per-site, per-parameter readings at 5-60 minute intervals, retrievable from October 2007 onward. - keyless public api — An API usable without registration, keys or payment. - daily values service — USGS's summarized daily time series condensing each site-parameter to one value per day. - provisional data disclaimer — USGS labels recent real-time readings provisional until reviewed, and the disclaimer bars their use in legal or regulatory decisions until approval.