welshman/skills/welshman-router/SKILL.md

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name: welshman-router description: Use this skill when working with @welshman/router: relay selection, routing strategies, scenario-based relay routing, or choosing which relays to use for reads/writes.

welshman/router — Relay Selection

@welshman/router provides scenario-based relay selection for nostr clients. It answers the question "which relays should I use for this operation?" by scoring candidate relays based on pubkey relay lists, relay quality, and configurable fallback policies. It sits between @welshman/util (types/helpers) and @welshman/net (actual relay connections), and is wrapped by @welshman/app for full-stack usage.

Installation

npm install @welshman/router
# or
pnpm add @welshman/router
yarn add @welshman/router

Peer dependencies: @welshman/lib, @welshman/net, @welshman/util.

Key Exports

Router (class)

The main entry point. Use as a singleton via Router.configure() + Router.get(), or instantiate directly with options.

Method	Description
Router.configure(options)	Merge options into the global routerContext
Router.get()	Return a Router instance using the global context
new Router(options)	Create a router that overrides specific options from the global context

RouterOptions (all optional):

Option	Signature	Description
getUserPubkey	() => string | undefined	Current user's pubkey
getPubkeyRelays	(pubkey, mode?) => string[]	Relays for a pubkey; mode is "read", "write", or "messaging"
getDefaultRelays	() => string[]	Fallback relays of last resort
getIndexerRelays	() => string[]	Relays that index profiles and relay lists (NIP-65)
getSearchRelays	() => string[]	Relays supporting NIP-50 search
getRelayQuality	(url) => number	Quality score 0–1 for a relay (affects selection ranking)
getLimit	() => number	Max relays returned by getUrls() (default: 3)

Default behavior: if getPubkeyRelays is not configured, the router falls back to querying the local Repository (from @welshman/net) for kind-10002 events.

Router Scenario Methods

All return a RouterScenario. Naming convention: For* = relays to write to (so others can read), From* = relays to read from (author's outbox).

Method	Description
FromRelays(relays)	Use an explicit list of relay URLs
ForUser()	User's read relays (where others can send things to the user)
FromUser()	User's write relays (user's outbox)
MessagesForUser()	User's messaging relays (NIP-17 DMs)
ForPubkey(pubkey)	A pubkey's read relays
FromPubkey(pubkey)	A pubkey's write relays (outbox)
MessagesForPubkey(pubkey)	A pubkey's messaging relays
ForPubkeys(pubkeys)	Merged read relays for multiple pubkeys
FromPubkeys(pubkeys)	Merged write relays for multiple pubkeys
MessagesForPubkeys(pubkeys)	Merged messaging relays for multiple pubkeys
Event(event)	Event author's write relays (where the event lives)
Replies(event)	Event author's read relays (where replies should be sent)
PublishEvent(event)	Author's outbox + mentioned pubkeys' read relays; hard-limits to 30
Quote(event, id, hints)	Best relays to find a quoted event; checks tag relay hints and author pubkey from tag
EventParents(event)	Relays for fetching parent events (from ancestor tags + mentioned pubkeys)
EventRoots(event)	Relays for fetching root events
Search()	Search relays
Index()	Indexer relays
Default()	Default/fallback relays
merge(scenarios)	Combine multiple scenarios into one

RouterScenario (class)

Immutable builder — every builder method returns a new instance. Terminal methods (getUrls(), getUrl()) return relay URLs, not instances.

Method	Description
getUrls()	Execute selection; returns string[]
getUrl()	Returns the first selected URL or undefined
limit(n)	Override max relay count for this scenario
weight(scale)	Multiply all selection weights by scale
policy(fn)	Set fallback policy
allowLocal(bool)	Allow ws://localhost / ws://127.* URLs (default: false)
allowOnion(bool)	Allow .onion URLs (default: false)
allowInsecure(bool)	Allow plain ws:// non-onion URLs (default: false)
filter(fn)	Filter the internal Selection[]
update(fn)	Map over the internal Selection[]

Fallback Policies

Applied after relay scoring when not enough relays are found. Draw from getDefaultRelays.

Export	Behavior
addNoFallbacks	Never add fallbacks (default)
addMinimalFallbacks	Add 1 fallback only if zero relays were selected
addMaximalFallbacks	Fill remaining slots up to the limit

Filter Selection

Export	Description
getFilterSelections(filters, rules?)	Returns RelaysAndFilters[] — optimized relay+filter combos for a subscription
RelaysAndFilters	{ relays: string[], filters: Filter[] }
defaultFilterSelectionRules	The default ordered rule array
getFilterSelectionsForSearch	Rule: search filters → search relays (weight 10)
getFilterSelectionsForWraps	Rule: kind-1059 wraps without authors → user messaging relays
getFilterSelectionsForIndexedKinds	Rule: kinds 0/3/10002/10050 → indexer relays
getFilterSelectionsForAuthors	Rule: author filters → each author's outbox (split into up to 30 chunks)
getFilterSelectionsForUser	Rule: low-weight (0.2) baseline that always fires for every filter → user's read relays. It is not conditional on other rules failing.

Other Exports

Export	Description
INDEXED_KINDS	[PROFILE, RELAYS, MESSAGING_RELAYS, FOLLOWS] — kinds routed to indexers
makeSelection(relays, weight?)	Create a Selection object; validates and normalizes URLs
Selection	{ weight: number, relays: string[] }
FallbackPolicy	(count: number, limit: number) => number
routerContext	The global mutable options object updated by Router.configure()

Common Patterns

1. Configure once at app startup

Router.get() is the primary entry point — it returns a Router instance using the global routerContext. Call Router.configure() once at startup to set options, or assign directly to routerContext for individual overrides.

import {Router} from '@welshman/router'

Router.configure({
  getUserPubkey: () => myStore.userPubkey,
  getPubkeyRelays: (pubkey, mode) => myStore.getRelaysForPubkey(pubkey, mode),
  getDefaultRelays: () => ['wss://relay.example.com/', 'wss://relay2.example.com/'],
  getIndexerRelays: () => ['wss://indexer.example.com/', 'wss://indexer2.example.com/'],
  getSearchRelays: () => ['wss://search.example.com/', 'wss://search2.example.com/'],
  getRelayQuality: (url) => myStore.getRelayQuality(url),
  getLimit: () => 5,
})

When using @welshman/app, it pre-configures Router automatically. The two most common customization points when using @welshman/app are getDefaultRelays and getIndexerRelays, which you can assign directly on routerContext:

import {routerContext} from '@welshman/router'

routerContext.getDefaultRelays = () => [
  'wss://relay.example.com/',
  'wss://relay2.example.com/',
]

routerContext.getIndexerRelays = () => [
  'wss://indexer.example.com/',
  'wss://indexer2.example.com/',
]

2. Fetch events from specific pubkeys

import {Router} from '@welshman/router'

const relays = Router.get().FromPubkeys(['pubkey1', 'pubkey2']).getUrls()
// relays is string[] — pass to your subscription

3. Publish an event

import {Router} from '@welshman/router'
import type {TrustedEvent} from '@welshman/util'

function getPublishRelays(event: TrustedEvent): string[] {
  return Router.get().PublishEvent(event).getUrls()
  // Automatically includes author's outbox + mentioned pubkeys' read relays
  // Hard-limited to 30 relays for deliverability
}

4. Find a quoted/referenced event with fallbacks

import {Router, addMaximalFallbacks} from '@welshman/router'
import type {TrustedEvent} from '@welshman/util'

function getQuoteRelays(event: TrustedEvent, quotedId: string, hints: string[]) {
  return Router.get()
    .Quote(event, quotedId, hints)
    .policy(addMaximalFallbacks)
    .limit(8)
    .getUrls()
}

5. Common scenario cheat-sheet

import {Router} from '@welshman/router'

const router = Router.get()

// Read relays for the current user (where others deliver events to you)
router.ForUser().getUrls()

// Write relays for the current user (your outbox)
router.FromUser().getUrls()

// Best relays to deliver an event to a pubkey (their inbox)
router.ForPubkey('pubkey').getUrls()

// Best relays to fetch events authored by a pubkey (their outbox)
router.FromPubkey('pubkey').getUrls()

// Indexer relays (profiles, relay lists)
router.Index().getUrls()

// Cap relay count for this scenario only
router.ForPubkey('pubkey').limit(3).getUrls()

// Merge multiple scenarios; relay URLs are deduplicated when getUrls() is called
router.merge([
  router.FromUser(),
  router.Index(),
]).getUrls()

6. Build subscriptions with getFilterSelections

import {getFilterSelections} from '@welshman/router'
import type {Filter} from '@welshman/util'

const filters: Filter[] = [
  {kinds: [1], authors: ['pubkey1', 'pubkey2']},
  {kinds: [0], search: 'bitcoin'},
]

for (const {relays, filters} of getFilterSelections(filters)) {
  // Open one subscription per relay group
  myPool.subscribe(relays, filters)
}

7. Use a custom filter routing rule

import {
  Router,
  getFilterSelections,
  defaultFilterSelectionRules,
  type RelaysAndFilters,
} from '@welshman/router'
import type {Filter} from '@welshman/util'

// Add a rule that sends kind-1 to a dedicated relay
const myRule = (filter: Filter) => {
  if (!filter.kinds?.includes(1)) return []
  return [{filter, scenario: Router.get().FromRelays(['wss://notes.example.com/'])}]
}

const selections = getFilterSelections(filters, [myRule, ...defaultFilterSelectionRules])

Integration Notes

• @welshman/util — Router imports TrustedEvent, Filter, RelayMode, PROFILE, RELAYS, MESSAGING_RELAYS, FOLLOWS, WRAP, normalizeRelayUrl, and tag-parsing helpers. All relay URLs are normalized with normalizeRelayUrl and validated with isRelayUrl before use.
• @welshman/net — The default getPubkeyRelays implementation queries Repository.get() (the in-memory event store from @welshman/net) for kind-10002 events. Override it if you maintain relay lists elsewhere.
• @welshman/app — The app layer pre-configures Router using its own stores (relay lists, connection quality). If you use @welshman/app, call Router.configure only to override specific options; the app layer handles the rest.
• @welshman/lib — Used internally for utilities (sortBy, shuffle, uniq, etc.); no direct integration needed.

Gotchas & Tips

• Relay list events must be in the Repository for pubkey routing to work. The default getPubkeyRelays implementation reads kind-10002 (NIP-65) relay list events from the global in-memory Repository. If those events haven't been loaded — either from a local cache at startup or fetched from the network — the Router has no relay list data for that pubkey and silently falls back to default/indexer relays. When using @welshman/app, relay lists are fetched automatically as part of profile loading (loadRelayList, makeOutboxLoader). Without @welshman/app, you must fetch and load them yourself before calling pubkey-based scenarios.

• For* vs From*: ForPubkey returns a pubkey's read relays (where you send things for that pubkey to receive); FromPubkey returns their write relays (their outbox, where their events live). Use From* to fetch events, For* to deliver events.

• Default limit is 3. Set getLimit in Router.configure or call .limit(n) on a scenario if you need more. PublishEvent unconditionally overrides to 30.

• Scoring includes randomness. getUrls() introduces Math.random() in the scoring formula so that lower-quality or less-popular relays get occasional selection. Results are not deterministic across calls.

• addNoFallbacks is the default policy. If no relays are found for a scenario (e.g. no relay list for a pubkey) and you haven't set a policy, getUrls() returns []. Use addMinimalFallbacks or addMaximalFallbacks when you need a result even for unknown pubkeys.

• Insecure ws:// URLs are filtered by default. Only onion addresses (*.onion) are exempt from the TLS requirement. Pass .allowInsecure(true) to a scenario if you need to support plain websocket relays (e.g. local dev).

• getFilterSelections uses addMinimalFallbacks. Each resulting relay group will have at least one relay if getDefaultRelays is configured and returns relays. If getDefaultRelays is not configured or returns an empty array, the group may still be empty.

• routerContext is a shared mutable object. Router.configure() mutates it in place with Object.assign. new Router(options) merges the supplied options over the global routerContext (via mergeLeft), so any options not provided in options still fall back to whatever is in routerContext. For true isolation (e.g. in tests), pass a complete options object or reset routerContext first.

• Quote reads relay hints from event tags. It looks for a tag whose second element (t[1]) matches the quoted event ID, then extracts a relay hint from t[2] and an author pubkey from t[3]. Standard NIP-21/NIP-10 tag format.