# SpecId Types

## `SpecId.SpecId`

Ethereum specification identifiers, in the engine's declaration order.

A specification selects the instruction table, gas schedule, precompile set, and transaction handlers an EVM runs under.

**Source:** [src/evm/SpecId.ts](https://github.com/wevm/ox/blob/main/src/evm/SpecId.ts#L7)