NIP-40

Expiration Timestamp - adds an expiration tag to events so relays and clients can discard them after a specified time.

Import

import { nip40 } from 'nostr-core'
// or import individual functions
import {
  addExpiration,
  getExpiration,
  isExpired,
} from 'nostr-core'

nip40.addExpiration

function addExpiration(tags: string[][], expiration: number): string[][]

Adds an expiration tag (unix timestamp) to event tags. Replaces any existing expiration tag.

const oneHour = Math.floor(Date.now() / 1000) + 3600
const tags = nip40.addExpiration([], oneHour)
// [['expiration', '1710000000']]

nip40.getExpiration

function getExpiration(event: NostrEvent | EventTemplate): number | undefined

Gets the expiration timestamp from an event, or undefined if none.

const exp = nip40.getExpiration(event)
if (exp) console.log(new Date(exp * 1000))

nip40.isExpired

function isExpired(event: NostrEvent | EventTemplate, now?: number): boolean

Checks if an event has expired. Optionally pass a custom "now" timestamp.

if (nip40.isExpired(event)) {
  console.log('Event has expired, discard it')
}

How It Works

• The expiration tag contains a Unix timestamp after which the event should be considered expired
• Relays MAY discard expired events
• Clients SHOULD hide expired events
• Events without an expiration tag never expire
• The tag can be added to any event kind
• Useful for temporary announcements, ephemeral content, or time-limited offers