The getFeeForMessage RPC method allows you to estimate the fee the network will charge for processing a given transaction message. This is useful for understanding transaction costs before they are submitted to the network. Version Note: This method is available in solana-core v1.9 or newer. For older versions, consider using getFees.

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Common Use Cases

  • Fee Estimation: Determine the likely transaction fee (in lamports) for a specific message.
  • Cost Optimization: Analyze fees for different transaction structures or at different times.
  • User Interface Display: Show users an estimated transaction cost before they sign and send a transaction.

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Request Parameters

  1. message (string, required): The transaction message, base64 encoded. You can obtain this by compiling a transaction.
  2. config (object, optional): A configuration object with the following fields:
    • commitment (string, optional): Specifies the commitment level to use. Defaults to finalized.
    • minContextSlot (number, optional): The minimum slot at which the request can be evaluated.

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Response Structure

The result field of the JSON-RPC response is an object with the following structure:
  • context (object):
    • slot (u64): The slot at which the fee was evaluated.
  • value (u64 | null): The estimated fee in lamports. This can be null if the fee cannot be determined (e.g., if the blockhash used in the message is too old or invalid).

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Examples

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1. Estimate Fee for a Simple Transfer Message

This example demonstrates how to construct a simple transfer, compile its message, and then fetch the estimated fee. 
# First, you need a base64 encoded message. 
# This typically involves creating a transaction, compiling its message, 
# and then base64 encoding the serialized message.
# The example message below is illustrative.
# Replace "MESSAGE_BASE64_ENCODED" with your actual encoded message.
curl https://mainnet.helius-rpc.com/?api-key=<api-key> -X POST -H "Content-Type: application/json" -d \
  '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "getFeeForMessage",
    "params": [
      "MESSAGE_BASE64_ENCODED", // Replace with your actual base64 encoded message
      { "commitment": "processed" }
    ]
  }'

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Developer Tips

  • Message Construction: The key to using getFeeForMessage is to correctly construct and serialize the transaction Message. This involves setting the fee payer, instructions, and a recent blockhash.
  • Recent Blockhash: The message must be constructed with a recent blockhash. If the blockhash is too old, the value in the response might be null.
  • Fee vs. Priority Fee: This method returns the base network fee. It does not include any additional priority fees you might add to a transaction to increase its likelihood of being processed quickly during times of network congestion. Use getRecentPrioritizationFees to estimate priority fees.
  • Lamports: The fee is returned in lamports (1 SOL = 1,000,000,000 lamports).
  • Null Value: A null value for the fee can indicate issues with the message (e.g., invalid blockhash, malformed message) or that the node cannot calculate a fee for it at the given commitment level or slot.
This guide provides the necessary steps to utilize the getFeeForMessage RPC method for estimating transaction fees on the Solana network.