> ## Documentation Index > Fetch the complete documentation index at: https://docs.neynar.com/llms.txt > Use this file to discover all available pages before exploring further. # By its FID and target FID > Lookup a link by its FID and target FID. ## OpenAPI ````yaml get /v1/linkById openapi: 3.0.4 info: title: Farcaster Hub API version: 2.35.0 description: > Perform basic queries of Farcaster state via the REST API of a Farcaster hub. See the [Neynar docs](https://docs.neynar.com/reference) for more details. contact: name: Neynar url: https://neynar.com/ email: team@neynar.com servers: - url: https://snapchain-api.neynar.com security: - ApiKeyAuth: [] tags: - name: Info description: Operations related to hub information. - name: Casts description: Operations related to casts. - name: Reactions description: Operations related to reactions. - name: Links description: Operations related to links. - name: UserData description: Operations related to user data. - name: Fids description: Operations related to FIDs. - name: Storage description: Operations related to storage limits. - name: Usernames description: Operations related to usernames. - name: Verifications description: Operations related to verifications. - name: OnChainEvents description: Operations related to on-chain events. - name: Message description: Operations related to messages. - name: HubEvents description: Operations related to hub events. paths: /v1/linkById: get: tags: - Links summary: By its FID and target FID description: Lookup a link by its FID and target FID. operationId: lookup-user-relation parameters: - name: fid in: query description: The FID of the link's originator required: true schema: $ref: '#/components/schemas/FidSchema' - name: target_fid in: query description: The FID of the target user for this link required: true schema: $ref: '#/components/schemas/FidSchema' - name: link_type in: query required: true schema: $ref: '#/components/schemas/LinkType' responses: '200': description: The requested Link. content: application/json: schema: $ref: '#/components/schemas/LinkAdd' default: $ref: '#/components/responses/ErrorResponse' externalDocs: description: Lookup a link by its FID and target FID url: https://docs.neynar.com/reference/lookup-user-relation components: schemas: FidSchema: type: integer format: uint64 minimum: 1 description: > Farcaster ID (FID). A unique identifier assigned to each user in the Farcaster network. This number is permanent and cannot be changed. FIDs are assigned sequentially when users register on the network. example: 1 LinkType: type: string description: >- Defines the type of social connection between users. - follow: Establishes a following relationship where the user will receive updates from the target user in their feed default: follow enum: - follow example: follow LinkAdd: allOf: - $ref: '#/components/schemas/MessageCommon' - type: object properties: data: allOf: - $ref: '#/components/schemas/MessageDataLink' - type: object properties: type: $ref: '#/components/schemas/MessageType' required: - type required: - data MessageCommon: type: object properties: hash: title: Hash digest of data pattern: ^0x[0-9a-fA-F]{40}$ type: string example: '0xd2b1ddc6c88e865a33cb1a565e0058d757042974' hashScheme: $ref: '#/components/schemas/HashScheme' signature: title: Signature of the hash digest pattern: ^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$ type: string format: byte signatureScheme: $ref: '#/components/schemas/SignatureScheme' signer: title: Public key or address of the key pair that produced the signature pattern: ^0x[0-9a-fA-F]+$ type: string required: - hash - hashScheme - signature - signatureScheme - signer MessageDataLink: description: >- Represents a social graph connection between users in the Farcaster network. Currently supports following relationships between users. allOf: - $ref: '#/components/schemas/MessageDataCommon' - type: object required: - linkBody properties: linkBody: description: >- Contains the details of the social connection, including the type of relationship and the target user. allOf: - $ref: '#/components/schemas/LinkBody' MessageType: type: string description: >- Type of the MessageBody. - MESSAGE_TYPE_CAST_ADD: Add a new Cast - MESSAGE_TYPE_CAST_REMOVE: Remove an existing Cast - MESSAGE_TYPE_REACTION_ADD: Add a Reaction to a Cast - MESSAGE_TYPE_REACTION_REMOVE: Remove a Reaction from a Cast - MESSAGE_TYPE_LINK_ADD: Add a new Link - MESSAGE_TYPE_LINK_REMOVE: Remove an existing Link - MESSAGE_TYPE_VERIFICATION_ADD_ETH_ADDRESS: Add a Verification of an Ethereum Address - MESSAGE_TYPE_VERIFICATION_REMOVE: Remove a Verification - MESSAGE_TYPE_USER_DATA_ADD: Add metadata about a user - MESSAGE_TYPE_USERNAME_PROOF: Add or replace a username proof - MESSAGE_TYPE_FRAME_ACTION: A Farcaster Frame action default: MESSAGE_TYPE_CAST_ADD enum: - MESSAGE_TYPE_CAST_ADD - MESSAGE_TYPE_CAST_REMOVE - MESSAGE_TYPE_REACTION_ADD - MESSAGE_TYPE_REACTION_REMOVE - MESSAGE_TYPE_LINK_ADD - MESSAGE_TYPE_LINK_REMOVE - MESSAGE_TYPE_VERIFICATION_ADD_ETH_ADDRESS - MESSAGE_TYPE_VERIFICATION_REMOVE - MESSAGE_TYPE_USER_DATA_ADD - MESSAGE_TYPE_USERNAME_PROOF - MESSAGE_TYPE_FRAME_ACTION ErrorResponse: required: - code - details - errCode - metadata - name - presentable type: object properties: errCode: type: string presentable: type: boolean name: type: string code: type: integer details: type: string metadata: required: - errcode type: object properties: errcode: type: array items: type: string HashScheme: type: string description: > Type of hashing scheme used to produce a digest of MessageData. - HASH_SCHEME_BLAKE3: Default scheme for hashing MessageData default: HASH_SCHEME_BLAKE3 enum: - HASH_SCHEME_BLAKE3 SignatureScheme: type: string description: |- Type of signature scheme used to sign the Message hash - SIGNATURE_SCHEME_ED25519: Ed25519 signature (default) - SIGNATURE_SCHEME_EIP712: ECDSA signature using EIP-712 scheme default: SIGNATURE_SCHEME_ED25519 enum: - SIGNATURE_SCHEME_ED25519 - SIGNATURE_SCHEME_EIP712 MessageDataCommon: description: >- Common properties shared by all Farcaster message types. These properties provide essential metadata about the message's origin, timing, and network context. required: - fid - network - timestamp type: object properties: type: $ref: '#/components/schemas/MessageType' fid: title: Farcaster ID of the user producing the message description: >- The unique identifier (FID) of the user who created this message. FIDs are assigned sequentially when users register on the network and cannot be changed. type: integer format: uint64 example: 2 timestamp: description: >- Seconds since Farcaster Epoch (2021-01-01T00:00:00Z). Used to order messages chronologically and determine the most recent state. Must be within 10 minutes of the current time when the message is created. type: integer format: int64 example: 48994466 network: $ref: '#/components/schemas/FarcasterNetwork' LinkBody: description: >- Defines a social connection between users in the Farcaster network. Currently used to establish following relationships, allowing users to curate their content feed. type: object properties: type: $ref: '#/components/schemas/LinkType' displayTimestamp: title: Original Timestamp description: >- User-defined timestamp that preserves the original creation time when message.data.timestamp needs to be updated for compaction. Useful for maintaining chronological order in user feeds. type: integer format: int64 example: 48994466 targetFid: $ref: '#/components/schemas/FidSchema' required: - type - targetFid FarcasterNetwork: type: string description: |- Farcaster network the message is intended for. - FARCASTER_NETWORK_MAINNET: Public primary network - FARCASTER_NETWORK_TESTNET: Public test network - FARCASTER_NETWORK_DEVNET: Private test network default: FARCASTER_NETWORK_MAINNET enum: - FARCASTER_NETWORK_MAINNET - FARCASTER_NETWORK_TESTNET - FARCASTER_NETWORK_DEVNET responses: ErrorResponse: description: An unexpected error response. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' securitySchemes: ApiKeyAuth: type: apiKey in: header name: x-api-key description: API key to authorize requests x-default: NEYNAR_API_DOCS ````