Prove the diff,or it doesn't ship.
Delta checks every pull request against the invariants your codebase already depends on, and blocks the merge the moment one breaks. You get a concrete counterexample, not an AI opinion.
AI writes a growing share of your code. It is fast, usually plausible, and every so often quietly wrong in a way your tests never notice. A change can compile, pass every test, read perfectly, and still break a guarantee the whole system depends on.
Tests assert that specific inputs produce specific outputs. Invariants are the properties that must hold for all inputs, on every path: things like balance >= 0, idempotent(retry), and auth before mutation. Most codebases depend on hundreds of them, and almost none are written down.
Delta mines those invariants, proves each one catches a real regression, and enforces them on every pull request. It never writes your code. When the gate fails, it hands back the shrunk input that breaks the promise, a fact you can paste straight into a test, not a paragraph of model reasoning.
Three steps from your repo to a gate that holds.
Read the code, draft the properties.
Delta reads each function and proposes candidate invariants: the properties that hold today, written as executable checks. You author nothing.
Mutate the code, keep what catches it.
Each candidate is run against a deliberately broken version of your code. Only the properties that catch the injected bug survive. Proofs, not opinions.
Diff the PR, block the regression.
On every pull request, Delta re-runs only the invariants the diff touches. Pass, and the merge proceeds. Fail, and it blocks with a counterexample.
Watch a plausible diff get stopped.
A refactor drops a balance check it judged redundant. Tests stay green. The invariant doesn't.
def withdraw(account, txn): """Debit txn.amount from the account.""" amt = txn.amount if not account.active: raise AccountClosed(account) if account.balance < amt: raise InsufficientFunds(txn) account.balance -= amt ledger.record(txn, -amt) return Receipt(txn, account.balance)
The guarantees that hold your system together.
Money never lies
Balances stay non-negative, totals reconcile, refunds never exceed charges.
Retries are safe
A request replayed under failure produces one effect, never two.
Auth comes first
Every mutation is checked before it runs, on every path, not just the happy one.
Order under load
Interleaved operations converge to the same state a serial run would.
Shapes hold
Serialization round-trips, migrations preserve meaning, contracts stay intact.
Sequence matters
Steps that must precede others always do: tax before discount, write before read.
Built for the procurement review.
Your code never trains a model.
Delta is a verification layer, not a training pipeline. Your source is used to mine and check invariants, nothing else, ever.
Runs where your code lives.
Cloud-default with model access included, or a VPC / self-host tier for teams whose code can't leave their environment.
A required check, nothing more.
Delta installs as one CI gate on your pull requests. No agents in your repo, no write access, no keys for you to rotate.
Block the next bad merge.
Delta is in a closed private beta. Connect a repository and we'll get your invariants mined, proven, and gating your pull requests.