# The API Co-Signer

For advanced automation, the **API Co-Signer** acts as a robotic team member.

* **Role:** It holds one of the MPC key shares on your own infrastructure.
* **Function:** It automatically signs transactions that meet specific policy criteria (e.g., "Auto-approve user withdrawals under $500").
* **Sovereignty:** By running a Co-Signer, you ensure that Keystone cannot move funds without your server's explicit cryptographic consent.


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