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Tanveer

LegacyLift

Modernise legacy systems. Prove nothing broke.

LegacyLift turns decades-old code into modern, tested software. It learns every business rule, migrates one piece at a time with a person approving each change, and proves the new system behaves exactly like the old one.

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Founder
Tanveer
Status
Building full-time

It began as a 5-day build at the UK AI Agent Hackathon × Conduct AI, Imperial College London.

Most migrations start with guesswork and end with a leap of faith. LegacyLift replaces both.

Rewriting old code is the easy part. Doing it without losing the rules, without a risky cutover, and with proof it still works. That is what a serious migration actually needs.

Generic translators convert syntax and quietly lose the intent. LegacyLift carries every rule across (fees, eligibility, the awkward edge cases), each traced back to the decision that set it.

Late-payment fee: cap at £25Finance

set in 2019 · regulatory cap · carried across unchanged

Understand it. Migrate it. Prove it.

Product demo · sample programs ACCTINT and FEECALC

  1. See what the old code actually does.

    LegacyLift reads the source, extracts the business rules buried inside, and maps how everything connects, so nothing important is lost in translation.

    • Parses COBOL, Java and VB6
    • Business rules with source citations
    • Risk-scores every unit

    ACCTINT

    • callsINTCALC
    • callsDATEUTIL
    • readsACCTREC

    Business rules found

    • Interest tiers by balance bandFinance
    • Senior bonus over age 65Finance
    • Dormant after 12 months inactiveOps

  2. Rewrite it, with a human in control.

    Modern code, generated one piece at a time and reviewed old versus new. A person approves every change before it ships. Nothing merges on trust.

    No big-bang cutover, no black box. The work stops at every piece for a person to approve, edit, or reject. You stay in control of your own system.

    • Migrates chunk by chunk
    • A human approval gate on every merge

    FEECALC.CBL

    every change · no exceptions

    Legacy · COBOL
    0000-MAIN.  MOVE 0 TO LK-FEE.  IF ACCT-TYPE = 'S'    GOBACK.  PERFORM 2000-FEE.
    Migrated · Python
    def main_0000(rec):  lk_fee = Decimal("0.00")  if rec.acct_type == "S":    return lk_fee  lk_fee = fee_2000(rec)

  3. Prove the new system still behaves.

    The rewrite is replayed against the real behaviour of the old system and compared field by field.

    Every chunk passes

    • Static analysis
    • Adversarial AI review
    • Generated tests that execute

    Legacy

    Migrated

    VectorLegacy = MigratedΔ
    ACC001standard1,201.500.00
    ACC004senior tier5,006.250.00
    ACC005dormant790.000.00
    ACC007premium25,041.670.00
    ACC010closed0.000.00

Fidelity Replay.

A differential verification engine proving behavioural equivalence before migrated code ships.

Fidelity Replay shows the new system behaves exactly like the old, field by field, and signs the result. Something you can hand to risk and audit that actually holds up.

byte-exact
behaviour comparison, no fudge
signed
attestation on every result
5 gates
Value · Sequence · Store · Determinism · Attested

Proof, not promises.

The result is sealed with a signed record your risk team can verify. Something you can hand to risk and audit that actually holds up.

100.0%

behavioural equivalence

signed ed25519

  • Value
  • Sequence
  • Store
  • Determinism
  • Attested

Independent, reproducible, and signed. Ready for risk and audit.

Replay can teach the migrator, or certify the result. Never both in the same lineage.

The Independence Rule. A validator that grades a rewrite against the same data that produced it is marking its own homework. LegacyLift keeps the two apart, so a passing score means something to your model-risk team and to an auditor.

Built for banks, government, and the systems that can’t go down.

It found the bug nobody would notice.

COBOL silently cuts off numbers that overflow their field. A modern rewrite doesn’t, so the new system quietly returns different numbers. On a real COBOL program, LegacyLift caught exactly that, before it shipped.

functions
116
business rules
49
Mapped from AWS’s CardDemo mainframe codebase.

Your source stays yours.

Bring your own key. Client source never touches LegacyLift infrastructure.

Legacy systems, modernised and proven.

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