Optimism

Optimism

eth_call

eth_call executes a message call locally against the EVM without writing to the chain or spending gas. Use it for every read operation you can't satisfy with a balance / nonce / storage lookup — anything that requires running EVM bytecode.

When to reach for it

• Read ERC-20 / ERC-721 / ERC-1155 state (balanceOf, ownerOf, tokenURI, decimals, symbol).
• Query DEX pools for prices or reserves.
• Simulate the outcome of a transaction before submitting it.
• Probe contract behaviour with arbitrary state overrides (see below).

Parameters

eth_call takes a transaction object + a block reference:

The second argument is a block tag (latest, safe, finalized, etc.) or hex block number.

eth_call also accepts an optional state override as a third argument — a map from address to fake balance / nonce / code / storage. Useful for "what-if" simulations.

Response shape

The result is the raw return data of the executed function — a hex string you decode with the contract's ABI.

1{
2  "jsonrpc": "2.0",
3  "id": 1,
4  "result": "0x00000000000000000000000000000000000000000000015af1d78b58c4000000"
5}

Decoded as uint256, that's 25,000,000,000,000,000,000,000 — 25,000 with 18 decimals.

Quick recipes

ERC-20 selectors (call-data prefixes) you'll see most often:

Append the 32-byte padded argument(s) to the selector to build the data field.

Pitfalls

1. State at latest may differ from state at submission time. If you're using eth_call to validate transaction parameters, expect transient drift; re-validate on-chain.
2. State overrides are not portable. Not every provider supports the third argument — TheRPC does, but if your code might run against a different upstream, fall back to a pure eth_call.
3. Reverts surface as errors. A failed eth_call returns error.code = 3 with revert data attached — decode it the same way you decode revert reasons from eth_sendRawTransaction.

See also

• eth_estimateGas — estimate gas for a state-changing version of the same call.
• eth_sendRawTransaction — actually submit the transaction once the read confirms validity.
• eth_getStorageAt — direct storage-slot read, no bytecode execution.

1curl https://optimism.therpc.io \
2  -X POST \
3  -H 'Content-Type: application/json' \
4  -d '{"jsonrpc":"2.0","id":1,"method":"eth_call","params":[{"to":"0x2260FAC5E5542a773Aa44fBCfeDf7C193bc2C599","data":"0x70a082310000000000000000000000006E0d01A76C3Cf4288372a29124A26D4353EE51BE"},"latest"]}'