Phylax and Titan Add App-Level Checks to Ethereum Blocks

Phylax and Titan Builder are checking Ethereum transactions against rules written by applications, a block-by-block safeguard that can keep transactions violating those rules from being included.

The checker runs while Titan assembles a block and can exclude a transaction that breaks an app’s stated limit. For example, an app could cap a single withdrawal at 50% of a vault’s assets. The protection applies only to risks an app has described in its rules.

An app can configure protected functions to fail in blocks that have not passed Titan’s check. That setting is intended to prevent users from reaching a protected function through a block that did not receive the check. Titan’s checks run only on blocks it builds, so they do not cover Ethereum blocks generally.

During the 24 hours before Nov. 10, Titan built about 53% of the blocks validators accepted from outside builders instead of assembling themselves. The figure measures Titan’s share of externally built blocks validators accepted, not its share of all Ethereum blocks. The protection therefore depends both on Titan building a block and on an app having a rule that applies to the transaction.

Lighter and Derive are Phylax’s first customers, with almost $1 billion under protection. On Linea, the Ethereum layer 2 network, Phylax has been offered as an opt-in since January, and Denaria enrolled. Denaria lost about $166,000 on April 5 in an accounting bug. Its only Phylax rule targeted bad debt, which the exploit did not create, so that rule did not trigger.

Apps must write and revise their own rules. The checker adds a tripwire alongside audits, but it addresses only outcomes covered by an app’s rules; it does not automatically identify every exploit. The system also has no cryptographic proof yet that a check ran, leaving users to trust Titan to perform it on the blocks it builds.