Nostr Flash — Custom Event Kinds

Published Jul 1, 2026

Regular (non-replaceable) event representing an ephemeral photography post.

Tag	Description
`url`	Direct URL to the image file (Blossom CDN)
`m`	MIME type of the image (`image/webp`, `image/jpeg`, etc.)
`x`	SHA-256 hex hash of the image file
`dim`	Image dimensions in `WxH` format
`lifetime`	Survival timer in seconds (e.g. `3600` = 1 hour)
`alt`	Accessibility caption (≤280 chars)
`t`	Hashtag for categorisation
`imeta`	Full Blossom image metadata (NIP-94 compatible)
`encrypted`	Set to `nip44` when content is NIP-44 encrypted
`p`	Hex pubkey of the encrypted recipient (for private posts)

Public posts: Human-readable caption text.
Private posts: NIP-44 encrypted JSON payload containing { "caption": "...", "imageUrl": "..." }.

Regular (non-replaceable) reaction event that extends the survival timer of a flash post.

Tag	Description
`e`	Hex event ID of the flash post being boosted
`p`	Hex pubkey of the flash post author
`extension`	Number of seconds to add to the post's survival timer
`rating`	Optional score (1–5) for quality rating

Optional free-text comment (may be empty).

expiresAt = (event.created_at + parseInt(lifetime_tag) + sum(extension_tags_from_boosts)) * 1000
isExpired = Date.now() > expiresAt

Expired events are hidden from the active feed and shown in the Archive (read-only).