A gas estimate failure may be a contract revert

Do not respond to every estimateGas error by doubling the gas limit. Estimation executes a proposed call under node rules; the call may be invalid before resource limits become relevant.

The Ethereum JSON-RPC reference defines eth_estimateGas as an estimate for transaction execution. It is not a repair service for a missing approval, an expired deadline or calldata sent to the wrong contract.

Inspect execution inputs first

1. Verify the RPC chain and the sender used for the quote.
2. Compare the sender's token and native balances with the requested spend and fees.
3. Check the exact spender's allowance.
4. Confirm the route has not expired and the output constraint remains valid.
5. Preserve native value and the complete calldata.

Next, run an ordinary call simulation and inspect available revert data. A decoded contract error can identify the failure, but an empty or nested RPC error is not proof of an out-of-gas condition. Retain the original provider code and a redacted diagnostic record.

When a larger limit is justified

Increasing a limit can help when evidence points to an underestimation or a known execution overhead, and the transaction remains semantically valid. Apply a documented, bounded margin rather than repeatedly escalating until a node accepts the request.

If estimation succeeds but the sender cannot afford the fee ceiling, lowering the input amount or obtaining native currency may be required. Increasing gas would make that constraint worse.

Keep estimation failures separate from a mined transaction that exhausted gas. The latter has a receipt and paid execution cost; the former may never have reached the network. Different evidence calls for different user messages and incident metrics.