eth_feeHistory

eth_feeHistory returns fee-market data for a contiguous range of blocks ending at newestBlock on Polygon mainnet (chain id 0x89 / 137). For each block in the window it reports the base fee per gas, the gas-used ratio, and — when you pass rewardPercentiles — the effective priority fee (tip) at each requested percentile. The response also includes the projected base fee for the block immediately after the window, so the baseFeePerGas array always has one more entry than the number of blocks requested.

This is the primary input for a bot fee strategy: read recent base fees to anticipate the next block's base fee, and read tip percentiles to pick a maxPriorityFeePerGas that matches how aggressively you want a transaction included. A common pattern is to request the last few blocks at the [10, 50, 90] percentiles and choose a tip from the median or upper band depending on urgency. Since Polygon's post-Bhilai fee market keeps base fees higher and more volatile than Ethereum's, sampling a short recent window each block is usually preferable to a single spot price from eth_gasPrice.

All numeric values are returned as 0x-prefixed hexadecimal strings (wei), including the entries inside the reward arrays. The gasUsedRatio field is the exception — it is a JSON number between 0 and 1.

Positional params array, in order:

Response fields

See errors.md for the full error envelope, the error.data fields, and handling guidance.

JavaScript (fetch)

const res = await fetch("https://api.triport.io/v1/polygon", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.TRIPORT_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    jsonrpc: "2.0",
    id: 1,
    method: "eth_feeHistory",
    params: ["0x4", "latest", [10, 50, 90]],
  }),
});


const { result } = await res.json();


// Suggest a tip from the median (50th percentile) of the most recent block.
const recentReward = result.reward.at(-1);
const medianTip = parseInt(recentReward[1], 16);
const nextBaseFee = parseInt(result.baseFeePerGas.at(-1), 16);
console.log({ nextBaseFee, medianTip });

TypeScript SDK (@triport/sdk)

import { Triport } from "@triport/sdk";


const client = new Triport({ apiKey: process.env.TRIPORT_API_KEY! });


interface FeeHistory {
  oldestBlock: string;
  baseFeePerGas: string[];
  gasUsedRatio: number[];
  reward?: string[][];
}


const history = await client.polygon.request<FeeHistory>("eth_feeHistory", [
  "0x4",
  "latest",
  [10, 50, 90],
]);


const nextBaseFee = parseInt(history.baseFeePerGas.at(-1)!, 16);
console.log("projected base fee (wei):", nextBaseFee);

Python (triport-sdk)

import os
from triport import Triport


client = Triport(api_key=os.environ["TRIPORT_API_KEY"])


history = client.polygon.request(
    "eth_feeHistory",
    ["0x4", "latest", [10, 50, 90]],
)


next_base_fee = int(history["baseFeePerGas"][-1], 16)
median_tip = int(history["reward"][-1][1], 16)
print("projected base fee (wei):", next_base_fee)
print("median tip (wei):", median_tip)

• baseFeePerGas is always one element longer than blockCount — the last entry is the predicted base fee for the block after newestBlock, which is what you feed into a maxFeePerGas estimate.
• gasUsedRatio values near 1.0 indicate full blocks and an upward-trending base fee; values well below 0.5 indicate the base fee is likely to fall.
• Keep blockCount small for real-time fee strategy. Because Polygon produces a block roughly every 2 s, a short window (4–32 blocks) tracks the live fee market closely; the 1024 maximum (~34 min) is for historical analysis, not per-block polling.
• Omitting rewardPercentiles returns a lighter response without the reward array — useful when you only need base-fee trends.
• All wei amounts (base fees and rewards) are hex strings; convert with base 16 before arithmetic. gasUsedRatio is already a decimal number.
• eth_feeHistory is available on the free tier (polygon_read_rpc category). Rate limiting is RPS-per-tier with burst; there is no daily quota. A -32003 rate_limited error means you should back off and retry shortly.
• For a single spot price instead of a window, see eth_gasPrice. For the suggested EIP-1559 tip directly, see eth_maxPriorityFeePerGas. To learn the current chain head before requesting a historical window, see eth_blockNumber.