Playbook 03

Agentic Legacy Code Modernisation

From technical debt to strategic advantage

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what it is

Modernise without the rewrite gamble

AI agents read your codebase, generate the specification, create test suites, and migrate – without throwing away 30 years of business logic. The economics of legacy modernisation have permanently changed.

the phased approach

Five phases of agentic modernisation

AI-powered discovery

Agents analyse code structure, extract business logic, map data flows, and identify compliance-relevant rules.

Test generation

Comprehensive test suites generated from code analysis – 0% to 80%+ coverage without relying on human memory.

Modernisation decision matrix

Automated scoring across eight criteria to determine approach: maintain, strangler fig, rewrite, or replace.

Continuous validation

Migration execution with continuous verification against generated test suites and emergency rollback procedures.

Compliance throughout

PII identification, audit trail preservation, and regulatory mapping built into every phase – not bolted on at the end.

70%

Innovation blocker
of orgs cite tech debt as blocker

80%+

Test coverage
achievable from zero

30-50%

Review reduction
code review cycle time reduction