Signature
A cryptographic proof that an Ethereum wallet authorized a specific message or transaction, required by Polymarket's CLOB API for all order submissions.
Definition
A cryptographic signature is a mathematical proof that the holder of a private key approved a specific piece of data. On Ethereum (and Polygon), signatures follow the EIP-712 typed data standard, which encodes the data being signed in a structured, human-readable format. Polymarket's CLOB requires a valid signature on every order to prove the trader authorized the trade.
In practice
Predtools bots use the @polymarket/clob-client and @polymarket/builder-signing-sdk packages to produce correctly formatted signatures automatically. Two signature types exist: L1 signatures from the root EOA wallet, and L2 signatures from the proxy-registered API key. Both are EIP-712 compliant but sign different data structures. Developers never need to implement signing manually — the SDKs handle key initialization and message signing given the private key from secrets.json. A malformed or expired signature causes the CLOB API to reject the order with an authentication error.