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The Kate RPC API provides methods for querying data availability proofs, commitments, and block metadata from the Avail blockchain. These endpoints are essential for light clients and validators to verify data availability without downloading entire blocks.

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Enabling Kate RPC

Kate RPC endpoints are disabled by default. To enable them, start your Avail node with the --enable-kate-rpc flag: 
avail-node --enable-kate-rpc

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Configuration

The Kate RPC service can be configured through the Deps struct with the following parameters:
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max_cells_size
usize
default:"10000"
The maximum number of cells that can be requested in a single query. This limit applies to kate_queryProof and kate_queryMultiProof methods.Configure via the --kate-max-cells-size command-line flag.
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rpc_enabled
bool
default:"false"
Enable or disable Kate RPC endpoints.Set via the --enable-kate-rpc flag.
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rpc_metrics_enabled
bool
default:"false"
Enable metrics collection for Kate RPC calls. Only use if you understand the performance implications.

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Available Methods

The Kate RPC API provides the following methods:

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Query Methods

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Type Definitions

The Kate RPC API uses the following core types:

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Rows

pub type MaxRows = ConstU32<64>;
pub type Rows = BoundedVec<u32, MaxRows>;
A bounded vector of row indices, limited to a maximum of 64 rows per request.

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Cells

pub type MaxCells = ConstU32<10_000>;
pub type Cells = BoundedVec<Cell, MaxCells>;
A bounded vector of cell coordinates, limited to the configured max_cells_size (default 10,000). Each Cell contains:
  • row - Row index in the data matrix
  • col - Column index in the data matrix

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Response Types

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GRow

pub type GRawScalar = U256;
pub type GRow = Vec<GRawScalar>;
A row of the data availability matrix, represented as a vector of 256-bit scalars.

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GDataProof

pub type GDataProof = (GRawScalar, GProof);
pub struct GProof([u8; 48]);
A data proof consisting of:
  • Cell data as a 256-bit scalar
  • KZG proof as a 48-byte array

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GMultiProof

pub type GMultiProof = (Vec<GRawScalar>, GProof);
An optimized multi-proof for multiple cells:
  • Vector of cell data as 256-bit scalars
  • Single aggregated KZG proof

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GCellBlock

pub struct GCellBlock {
    pub start_x: u32,
    pub start_y: u32,
    pub end_x: u32,
    pub end_y: u32,
}
Defines a rectangular region in the data matrix.

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Error Handling

Kate RPC methods return JSON-RPC errors with the following error code:
  • Error Code 1 (KateRPCError) - Generic Kate RPC error
Error messages include specific details about the failure:
  • "Requested block {hash} is not finalized" - Block must be finalized before querying
  • "Requested block {hash} has empty commitments" - Block contains no data commitments
  • "Cannot query ({n}) more than {max} amount of cells per request" - Exceeds max_cells_size limit
  • "Cannot fetch tx data at tx index {idx} at block {hash}" - Transaction index out of range

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Block Finalization Requirement

All Kate RPC methods require the queried block to be finalized. Queries for unfinalized blocks will return an error. This ensures that the returned proofs and commitments are immutable and can be safely relied upon.

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JSON-RPC Format

All Kate RPC methods use standard JSON-RPC 2.0 format: 
{
  "jsonrpc": "2.0",
  "method": "kate_methodName",
  "params": [...],
  "id": 1
}
The default endpoint is http://localhost:9944 for HTTP or ws://localhost:9944 for WebSocket connections.

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Use Cases

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Light Clients

Light clients use Kate RPC to:
  • Verify data availability without downloading full blocks
  • Sample random cells to detect data withholding
  • Validate specific transactions using data proofs

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Data Availability Sampling

Validators and fishermen use these endpoints to:
  • Perform DAS (Data Availability Sampling) on committed data
  • Generate fraud proofs when detecting invalid commitments
  • Reconstruct missing data from available cells

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Application-Specific Queries

Applications can:
  • Query specific transaction data with Merkle proofs
  • Verify inclusion of application data in blocks
  • Efficiently download only relevant portions of blocks

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