evm-fees-advisor

evm-fees-advisor is a REST + SSE API for EVM network gas fee estimation. It supports EIP-1559 (Ethereum mainnet, Polygon, BSC) and legacy gasPrice (Ethereum Classic), with per-transaction gas estimation via eth_estimateGas.

Use it when you need to:

• Get accurate maxFeePerGas + maxPriorityFee for EIP-1559 transactions
• Estimate gas cost per specific contract call
• Predict baseFee worst-case N blocks ahead to avoid stuck transactions
• Recover a stuck transaction with the correct minimum fee bump
• Plan a batch of transactions with deadline constraints

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Fee models

EIP-1559 (Ethereum, Polygon, BSC)

{
  "feeModel": "eip1559",
  "currentBaseFeeGwei": 45.2,
  "fast":   { "maxPriorityFeeGwei": 2.0, "maxFeePerGasGwei": 100.0, "estimatedWaitBlocks": 1 },
  "medium": { "maxPriorityFeeGwei": 1.0, "maxFeePerGasGwei": 70.0,  "estimatedWaitBlocks": 3 },
  "slow":   { "maxPriorityFeeGwei": 0.5, "maxFeePerGasGwei": 55.0,  "estimatedWaitBlocks": 6 },
  "updatedAt": "..."
}

maxFeePerGas = currentBaseFee × 2 + maxPriorityFee (worst-case for next block).

Legacy gasPrice (Ethereum Classic)

{
  "feeModel": "legacy",
  "fast":   { "gasPriceGwei": 10.0, "estimatedWaitBlocks": 1 },
  "medium": { "gasPriceGwei": 6.0,  "estimatedWaitBlocks": 3 },
  "slow":   { "gasPriceGwei": 3.5,  "estimatedWaitBlocks": 6 }
}

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Endpoints

GET /fees

Current fee tiers (EIP-1559 or legacy format, depending on network).

GET /fee-advisor/next-base-fee?blocks=5 (EIP-1559 only)

BaseFee worst-case prediction for the next N blocks.

Assumes each block is 100% full → baseFee × 1.125 per block. Use worstCaseInNBlocksGwei + tip as your maxFeePerGas to guarantee inclusion within N blocks.

Returns HTTP 400 for legacy networks.

POST /fee-advisor/estimate

Calls eth_estimateGas against the node. Auto-detects transaction type:

data field	Detected type	Gas handling
empty	eth_transfer	Hardcoded 21,000 gas
starts with a9059cbb	erc20_transfer	Calls estimateGas
other	contract_interaction	Calls estimateGas

Returns estimatedGas, recommendedGasLimit (+20% buffer), txType, wouldRevert, and fee estimates per tier.

If the transaction would revert → HTTP 422 with ESTIMATE_GAS_FAILED.

POST /fee-advisor/deadline

Fee required to confirm within deadlineSec seconds at targetProbability.

curl -X POST .../fee-advisor/deadline \
  -d '{"deadlineSec": 120, "targetProbability": 0.95}'

POST /fee-advisor/stuck-tx

Recovery fee for a stuck EIP-1559 transaction. EVM nodes require minimum +10% on both maxFeePerGas and maxPriorityFee to accept a replacement.

Returns "action": "replace" with new values, or "action": "wait" if current fees are sufficient.

POST /fee-advisor/batch

Batch transaction planner. Same strategies as bitcoin-fees-advisor: minimize_cost, uniform, asap.

GET /fee-advisor/market

Full network state: baseFee, block utilization, pending tx count, priority fee percentiles (p10/p50/p90), baseFee history for last 10 blocks.

GET /fees/stream (SSE)

Real-time fee updates. Throttled to SSE_MIN_INTERVAL_MS (default: 30s). Heartbeat every 25s.

GET /events/stream?txids=0xabc (SSE)

Watch specific EVM transaction hashes: tx.confirmed, tx.replaced.

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Network specifics

Network	Fee model	Notes
Ethereum mainnet	EIP-1559	Standard volatility
Polygon PoS	EIP-1559	High baseFee volatility (spikes to 1000+ gwei). Aggressive worst-case in deadline calculations.
BSC	EIP-1559	BaseFee stable (~3 gwei). Priority fee dominates. Response includes a note.
Ethereum Classic	Legacy	No baseFee. next-base-fee endpoint returns HTTP 400.

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Billing

• Free - rate-limited requests
• PAYG / requests - per API call
• Subscription / credits - monthly request pool

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Next steps

• API Reference →
• Code Examples →
• Activate in Dashboard →

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Related reading: EVM Gas Fee Estimation Guide