The getBlocksWithLimit RPC method allows you to retrieve a list of confirmed block slot numbers, starting from a specified slot and returning up to a given limit. This is useful when you need a specific number of subsequent confirmed blocks from a certain point in the ledger.

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Common Use Cases

  • Fetching a Fixed Number of Subsequent Blocks: Get a defined number of block slots that were confirmed after a particular start slot.
  • Paginated Block Exploration: Retrieve blocks in chunks when analyzing a segment of the blockchain.
  • Recent Block Monitoring: Get the last N blocks from a known recent slot.

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Request Parameters

The getBlocksWithLimit method takes the following parameters:

  1. start_slot (u64, required): The first slot to consider (inclusive).
  2. limit (u64, required): The maximum number of block slots to return. The total number of slots queried (from start_slot up to limit blocks after it) must not exceed 500,000 slots.
  3. commitment (string, optional): Specifies the commitment level for the query. If omitted, the default commitment of the node is used. This is passed as the sole field in a configuration object as the last parameter.

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Response Structure

The result field of the JSON-RPC response will be an array of u64 integers. Each integer in the array represents a confirmed block slot number, starting from start_slot up to the specified limit.

  • Example: If start_slot is 5 and limit is 3, a possible result is [5, 6, 7].

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Examples

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1. Get a Limited Number of Blocks from a Start Slot

This example fetches a list of up to 5 confirmed block slots starting from slot 280000000.

curl https://mainnet.helius-rpc.com/?api-key=<api-key> -X POST -H "Content-Type: application/json" -d \
  '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "getBlocksWithLimit",
    "params": [
      280000000, 
      5 
    ]
  }'

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2. Get Blocks With Limit and a Specific Commitment Level

This example fetches up to 3 blocks starting from slot 290000000 using the confirmed commitment level.

curl https://mainnet.helius-rpc.com/?api-key=<api-key> -X POST -H "Content-Type: application/json" -d \
  '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "getBlocksWithLimit",
    "params": [
      290000000,
      3,
      { "commitment": "confirmed" }
    ]
  }'

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Developer Tips

  • Range Clarification: The limit parameter dictates the maximum number of block slots to return. The 500,000 slot constraint applies to the conceptual range scanned (i.e., from start_slot to start_slot + limit - 1). Ensure this conceptual range doesn’t exceed 500,000 slots, even if fewer actual blocks are found and returned within that range.
  • Node Data Availability: Nodes may not retain information for all historical slots. A very old start_slot might return fewer blocks than the specified limit, or an empty array, depending on the node’s ledger retention.
  • Block Confirmation: This method returns confirmed blocks. The exact set of blocks can vary slightly depending on the chosen commitment level and which node you query, especially for very recent slots.
  • Use Case Specificity: getBlocksWithLimit is ideal when you know the starting point and need a fixed number of subsequent blocks. If you need all blocks in a known slot range, getBlocks might be more appropriate.

This guide provides a clear overview of how to use the getBlocksWithLimit RPC method to list a specific number of confirmed block slots on the Solana network.