# concepts

- [hydrant vs tap](https://hydrant.klbr.net/concepts/vs-tap/index.md): design comparison, stream behavior
- [relay & seeding](https://hydrant.klbr.net/concepts/relay/index.md): multi-relay support, firehose seeding, crawler sources
- [retention](https://hydrant.klbr.net/concepts/retention/index.md): how event and record history ttls behave, and what `/stats` counts under them