Post or remove a reaction (like) on a Farcaster cast via the Neynar API v2
domain: farcaster.xyz · 5 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Create a Neynar API key and obtain an approved signer_uuid for the reacting account (same key that created the signer).
POST https://api.neynar.com/v2/farcaster/reaction with x-api-header and JSON {"signer_uuid":"<uuid>","reaction_type":"like","target":"<cast-hash-or-url>","target_type":"hash"}.
Verify by fetching the cast via GET /v2/farcaster/cast and confirming reactions.likes_count increased / the react entry appears.
To remove: DELETE https://api.neynar.com/v2/farcaster/reaction with the same fields and reaction_type like.
Use the SDK: await neynar.publishReactionToCast({signerUuid, reactionType:'like', castId}) for add, or removeReaction for delete.
Known gotchas
The signer must be approved and belong to the same API key; otherwise reaction writes are rejected.
target_type must match how you reference the target (hash vs url); omit or mismatch causes 4xx errors.
Reactions include like and recast — recast uses a different reaction_type value and also affects feed visibility.
Reaction endpoints rate-limit on writes; batch reads of reactions use GET /v2/farcaster/reactions endpoints.
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