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AI-assisted legacy modernisation

Retire a legacy system in slices, using AI agents to map the code and extract business rules while the old system keeps running.

Typical timing
5–6 weeks to plan, then 3-month slices
Engagement
Phased programme
Delivery framework
User researchDiscoveryAlphaBetaLive
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Objective

Replace an ageing, hard-to-change system without a risky big-bang cutover. AI agents accelerate the slow parts — understanding undocumented code, extracting business rules, generating tests — while senior engineers own every design decision and every line that ships.

You may need this if

  • A core system nobody wants to touch, and the people who understood it are leaving
  • Unsupported frameworks, databases or operating systems
  • Every change takes months and breaks something else
How it runs

Activities, step by step

The plan follows our delivery framework. Steps that do not apply to this kind of work are left out rather than padded.

  1. 01 · User research2 weeks

    Understand how it is really used

    • Interviews with users and support staff
    • Usage analytics to find the features that matter
    • Pain points and workarounds catalogued
  2. 02 · Discovery3–4 weeks

    Map, extract and plan

    • AI-assisted code mapping: dependencies, data access and execution paths
    • Business rules extracted and confirmed with domain experts
    • Strangler-fig roadmap with the first slice chosen
  3. 03 · Alpha6–8 weeks

    First slice

    • Characterisation tests that pin current behaviour
    • First capability rebuilt on the target architecture
    • Parallel running to prove equivalence
  4. 04 · Beta2–4 weeks

    Cut over the slice

    • Data migration rehearsed and reconciled
    • Traffic routed to the new service progressively
    • Old code path switched off
  5. 05 · LiveQuarterly increments

    Repeat, slice by slice

    • Next slice from the roadmap
    • Legacy footprint and run cost tracked down
    • Knowledge transferred to your engineers as we go

The discovery stands alone: you own the map and the roadmap whether or not we build.

Deliverables

What you keep at the end.

  • System map and business rules catalogue
  • Modernisation roadmap with slice sequence and costs
  • Characterisation test suite
  • Modernised services in production, slice by slice
  • Decommissioning plan for the legacy estate

Outcomes

What it is built to change.

  • Legacy risk reduced without a big-bang cutover
  • Change lead time cut from months to days
  • Documented knowledge that no longer lives in one person’s head

Often combined with

Every engagement starts with a 45-minute working session with the SME who would own the work. No deck.

Discuss AI-assisted legacy modernisation