payment_queryFeeDetails

Returns a detailed breakdown of fees for a given extrinsic on Bridge Hub. Unlike payment_queryInfo which returns the total fee, this method separates the fee into its component parts.

Use Cases

• Fee analysis - Understand fee composition for trustless ETH and ERC-20 bridging, cross-chain messaging, and parachain-to-Ethereum asset transfers
• Optimization - Identify which fee component dominates costs
• Debugging - Diagnose unexpected fee amounts

Parameters

Parameter	Type	Required	Description
extrinsic	Bytes	Yes	SCALE-encoded extrinsic (signed or unsigned)
blockHash	Hash	No	Block hash for fee calculation context

Returns

Field	Type	Description
inclusionFee	Option<InclusionFee>	Fee details (null for unsigned extrinsics)

InclusionFee Structure

Field	Type	Description
baseFee	Balance	Fixed base fee per extrinsic
lenFee	Balance	Fee based on encoded extrinsic length
adjustedWeightFee	Balance	Fee based on execution weight

Code Examples

cURL

curl https://api-bridge-hub-polkadot.n.dwellir.com/YOUR_API_KEY \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "payment_queryFeeDetails",
    "params": ["0x...encodedExtrinsic"],
    "id": 1
  }'

JavaScript

import { ApiPromise, WsProvider } from '@polkadot/api';

const provider = new WsProvider('wss://api-bridge-hub-polkadot.n.dwellir.com/YOUR_API_KEY');
const api = await ApiPromise.create({ provider });

// Create a sample transfer
const tx = api.tx.balances.transferKeepAlive(
  '5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty',
  1000000000000n
);

// Get fee details
const feeDetails = await api.rpc.payment.queryFeeDetails(tx.toHex());

if (feeDetails.inclusionFee.isSome) {
  const fee = feeDetails.inclusionFee.unwrap();
  console.log('Base fee:', fee.baseFee.toString());
  console.log('Length fee:', fee.lenFee.toString());
  console.log('Weight fee:', fee.adjustedWeightFee.toString());
}

await api.disconnect();

Python

import requests

url = 'https://api-bridge-hub-polkadot.n.dwellir.com/YOUR_API_KEY'

# Replace with actual encoded extrinsic
encoded_extrinsic = '0x...'

payload = {
    'jsonrpc': '2.0',
    'method': 'payment_queryFeeDetails',
    'params': [encoded_extrinsic],
    'id': 1
}

response = requests.post(url, json=payload)
result = response.json()['result']

if result['inclusionFee']:
    fee = result['inclusionFee']
    print(f"Base fee: {fee['baseFee']}")
    print(f"Length fee: {fee['lenFee']}")
    print(f"Weight fee: {fee['adjustedWeightFee']}")

Fee Components Explained

Component	Calculation	Optimization
Base fee	Fixed per extrinsic	Batch calls to share base fee
Length fee	length * lengthToFee	Minimize call data size
Weight fee	weight * weightToFee	Choose efficient operations

Related Methods

• payment_queryInfo - Get total fee estimate
• author_submitExtrinsic - Submit transaction
• state_call - Call TransactionPaymentApi directly