# Ethics and rate limits

The nostalgia index pulls its data from the [Wikimedia REST API](https://wikimedia.org/api/rest_v1/), a free public service. This page covers how the package keeps its requests polite and how to make them identify you.


# Identifying your requests

Wikimedia's [User-Agent policy](https://foundation.wikimedia.org/wiki/Policy:Wikimedia_Foundation_User-Agent_Policy) asks every client to send a descriptive `User-Agent` header with contact information. The package sends one with every request, but the default contains placeholder contact details. Edit `USER_AGENT` in `nostalgia_index.client` to use your own project URL and email.


# Keeping request volume low

The package requests only `agent=user` data, which excludes spiders. Historical pageviews don't change, so responses are cached on disk and each article and date range is downloaded only once. The cache lives in `~/.cache/nostalgia_index`; set the `NOSTALGIA_CACHE_DIR` environment variable to store it somewhere else.


*\[Rich HTML output -- view on the documentation site\]*


When the API responds with a 429 (too many requests) or a server error (500, 502, 503, or 504), the request is retried with exponential backoff, up to four times.


# Recap

Replace the placeholder contact details in `USER_AGENT` before making regular requests. The disk cache and backoff retries keep load on Wikimedia low, and `NOSTALGIA_CACHE_DIR` controls where cached responses are stored.