Large-scale migrations · Mainframe

Mainframe modernization, end to end

COBOL, JCL, PL/I, DB2 to your modern stack. Parity proof at every step, built on accurate, code-derived understanding of how your applications actually behave.

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Why mainframe modernization stalls

Mainframe modernization is some of the highest-risk work in any enterprise. The same three things stall every program.

Business behavior is buried in code

Decades of COBOL, JCL, PL/I, and DB2 carry the rules of the business. Logic lives in thousands of programs, jobs, and data flows, with no source of truth and no specification to migrate against.

Auto-translators stop at the easy part

Tools that translate COBOL to Java produce code that compiles. They don't produce code that behaves the same way. The output runs. The business doesn't run the same.

Parity is impossible to prove

Boards, regulators, and risk committees need traceable evidence that the modernized system matches the original. Without code-derived understanding, parity is asserted, not proved.

How we do it

Three layers, working together

Existing approaches fall short. Auto-translators preserve syntax, not behavior. Structural analysis describes structure, not what the application does. AI alone hallucinates on legacy code. Consultants alone don't scale. We run three layers that establish accurate, code-derived understanding before any line of code is migrated.

Layer 01

Deterministic analysis

Our proprietary engine analyzes the complete codebase. COBOL, PL/I, JCL, DB2, copybooks. Programs, jobs, data flows, cross-application dependencies. Established deterministically from source code, not inferred.

Mainframe inventory
acme.banking.core12.4M LOC
├─ COBOL programs4,201
├─ JCL jobs1,847
├─ DB2 tables612
├─ Copybooks3,200
├─ Cross-program flows2,140 mapped
└─ Dead programs23% of inventory
312 end-to-end flows · 1,820 decision paths · 8,400+ rules
Layer 02

AI for scale

Anchored in the deterministic analysis, our AI agents apply verified migration patterns. COBOL paragraphs to Java service methods, JCL jobs to scheduled workflows, DB2 access to repository patterns. Each pattern validated once against the original business behavior, then scaled.

Migration pattern
CUSTONB03 (COBOL) → BillingService.calculateRisk() (Java)
- COMPUTE RISK-SCORE = CUST-INCOME / CUST-DEBT.
- IF RISK-SCORE > 0.7
- PERFORM ESCALATE-CASE
- ELSE
- PERFORM APPROVE-CASE.
+ public RiskAssessment calculateRisk(Customer c) {
+ double score = c.getIncome() / c.getDebt();
+ return score > 0.7 ? escalate(c) : approve(c);
+ }
Pattern: COBOL paragraph → Java service method · Applied 184x
Layer 03

SMEs and enterprise context

Senior engineers validate the migration in context, catch the edge cases auto-translators miss, and lock down the regional variations, compliance rules, and deprecated paths that determine whether the modernized system behaves the same as the original.

Enterprise enrichment
Enterprise architect
Customer.OnboardNew · UK retail only

This flow handles UK retail customers. EU retail follows a separate path (CUSTONB_EU). The split was introduced in 2018 for GDPR and has not been re-evaluated since. Confirmed before any consolidation work.

Senior platform engineer
rule.compliance.kyc · escalation

Sanction-screen escalation rule was updated in 2023 for OFAC. The change is in CUSTONB03 lines 412–438 and is not reflected in the original specification documents. Captured as evidence-backed addendum.

Engagement model

Your mainframe modernization, in four scoped stages

Four stages. Fixed price per stage. Commit one step at a time, with validation evidence at every one.

01

Assessment

Snapshot of your mainframe estate. Program and job inventory, technology surface, dependency graph, scope of work. Scoped plan, risks, and success criteria.

What you receive
  • Mainframe estate snapshot
  • Scoped plan
  • Risk register
  • Locked success criteria
02

Specification

Reverse engineer business and technical behavior directly from the complete codebase. End-to-end flows mapped, business rules extracted from executable logic, decision paths and data lineage documented.

What you receive
  • End-to-end process flows
  • Extracted business rules
  • Data lineage across programs and jobs
  • Cross-application dependencies
03

Modernization

Migrate the code to your target stack. Refactor where the original structure won't survive the move off the mainframe. Parity validated per migration unit, with visible progress throughout.

What you receive
  • Migrated code on target stack
  • Refactored services where needed
  • API and integration code
  • Parity validation evidence
04

Enablement

Keep evolving the modernized system independently. Parity test suite, playbooks, training, and a queryable knowledge base of the original mainframe, handed off to your team.

What you receive
  • Parity test suite
  • Migration playbooks
  • Team training
  • Queryable knowledge base

Each stage builds on the last. Fixed price, with validation evidence at every step.

What you get

A workspace, not a stack of files

Every deliverable lives in one place. Yours to keep, queryable by your tools.

Delivered change

  • Migrated code on target stack
  • Refactored services where needed
  • API and integration code
  • Parity validation evidence

System understanding

  • Program and job inventory
  • Dependency and data lineage maps
  • Dead-code analysis
  • End-to-end flows and business rules derived from code
  • Queryable by MCP

Enablement assets

  • Parity test suite
  • Migration playbooks
  • Team training
  • Queryable knowledge base

Modernize the mainframe. With proof.

Get in touch with our team. We'll talk through your mainframe estate, your target stack, and the right path off it.

Get in touch