What is Pessimistic Proof?
A pessimistic proof is a bridge safety check that assumes every connected chain may be broken. Before a withdrawal settles it proves the chain cannot take out more than it has put in: cumulative withdrawals must not exceed deposits net of pending exits. A chain that fails the check can only damage itself, never the shared bridge.
Also called: pessimistic proof · withdrawal invariant · max drain cap · bridge solvency proof
Formula
maxDrainCap = Σ deposits − Σ pending withdrawals
invariant: Σ withdrawals ≤ maxDrainCap
status = settled when the invariant holds, otherwise rejected — there is no partially settled state
Why 'pessimistic'
Optimistic and validity systems ask whether a chain's state transition was correct. A pessimistic proof asks a blunter question: even if this chain is entirely compromised, can it drain assets belonging to anyone else? By enforcing a per-chain accounting cap at the bridge it contains a failure to the chain that caused it — and that containment is what lets chains with different security models share one bridge.
What it means for settlement
For a data desk the practical reading is binary: a cross-chain bundle either satisfies the invariant and settles, or is rejected outright, with no half-settled state to reconcile. It is a solvency guard on the bridge's own books — not an attestation about the underlying asset. Custodian, issuer and redemption terms remain entirely separate questions.
Frequently asked questions
What does a pessimistic proof actually prove?
That a connected chain's cumulative withdrawals never exceed its deposits net of pending exits — so a compromised chain cannot withdraw assets belonging to other chains.
Is it the same as a validity proof?
No. A validity proof attests that a state transition executed correctly. A pessimistic proof assumes nothing about correctness and simply caps what a chain can remove from the shared bridge.
Where this shows up live
On the desk
What our numbers do and do not measure
Every figure on those pages carries its source and as-of time. Nothing is shown when the upstream is unavailable.
Related terms
- AggLayer — AggLayer is Polygon's cross-chain settlement layer.
- Atomic Settlement — Atomic settlement is all-or-nothing settlement: every leg of a transaction completes together or none do, with no partial or failed state.
- Proof of Reserve — Proof of reserve (PoR) is an independent, on-chain attestation that a tokenized asset is fully backed by the assets it claims to hold.
More in Settlement
Informational only · not financial advice. See the live numbers on the data desk, the sourcing rules in the methodology, or the day's stories in the newsroom. · ← All glossary terms