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Fenrir-s

github.com/rushmi0/Fenrir-s Nostr Open-source projectOpen source

Fenrir-s provides a Kotlin implementation of a Nostr relay, with its source code hosted on GitHub.

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github.com/rushmi0/Fenrir-s
Fenrir-s homepage screenshot

About Fenrir-s

Fenrir-s is an open source Nostr relay written in Kotlin that follows the Nostr Protocol. The project is aimed at personal use or small groups of friends. The relay's name, description, owner key, and contact address are set in a configuration file, and access rules can be adjusted. Installation uses Docker Compose, so Docker must be installed and running first.

Access rules are controlled by settings. By default, the relay accepts events from everyone. It can instead be limited to accounts the owner follows, and an optional Proof of Work requirement can be enabled. The default minimum difficulty of 32 is described as fairly high, and the source suggests lowering it or disabling the requirement. Local access uses a ws://localhost address. A public wss address requires an optional Cloudflare Tunnel. An optional setting can pull the owner's follow list from other relays, which involves connecting to external relays.

Key features

  • Supports NIP-01, 02, 04, 09, 11, 13, 15, 28, 45, and 50
  • Accepts events from everyone or only from followed accounts
  • Optional Proof of Work check with a configurable minimum difficulty
  • Relay name, description, owner npub, and contact set in a config file
  • Docker Compose setup with JVM 21 or native binary app options
  • Optional follow list sync from other relays through listed relay addresses
Best for: Individuals or small groups of friends who want to run their own Nostr relay with adjustable access rules.
Good for
  • Open source, with the source code hosted publicly on GitHub
  • Access policies such as follow-only acceptance can be configured
  • Installation is described as simple, using Docker Compose
Watch out for
  • Docker must be installed and running before the relay can be started
  • The default Proof of Work difficulty of 32 is described as fairly high
  • Remote access depends on firewall and port settings, and public addresses require an optional Cloudflare Tunnel

Fenrir-s at a glance

Type
Open-source project
Pricing
Not confirmed. Check the site
Open source
Yes · Source code
Language
English
Last checked
Oct 6, 2026 · Online when checked
Listed
Oct 5, 2026
open sourcedocker

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Fenrir-s FAQ

What needs to be installed before running Fenrir-s?
Docker must be installed and running before starting the relay, according to the installation steps.
Who can send events to the relay by default?
If no settings are changed, the relay is a public relay that accepts events from everyone. The ALL_PASS setting is true by default.
How can the relay be reached?
Locally, it is available at ws://localhost:6724 after Docker starts. A wss:// address through Cloudflare Tunnel is available only if that optional tunnel has been configured.
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Listing maintained by Chris McClure and the WebIndexly editors · Updated Oct 12, 2026 · How we rank