01
Map
See what is actually there.
Module, service, route, API, dependency, and integration inventory. Dead code candidates. Migration blockers. The map gets cleaner as we read.
Output:A versioned system map with provenance.
Legacy modernization, verified.
Modernize legacy software without breaking the business.
Grayhaven maps your legacy system, captures critical behavior, builds a verification harness, and ships bounded modernization increments with human-reviewed AI assistance.
Frontend
AngularJS, Vue 2, jQuery, old React
.NET
Framework, ASP.NET MVC, WebForms, WCF
Java
Spring monoliths, JEE, SOAP services
Why this matters
Old systems do not break because they are old. They break when teams change behavior they cannot see.
AI can write new code fast. The hard part is proving the new code preserves the billing rules, workflow quirks, integrations, reports, and edge cases the business already depends on.
A blind rewrite replaces known risk with unknown risk. Grayhaven does the opposite: map the system, capture behavior, and ship each change behind a parity check.
Map the system.
Capture behavior.
Change safely.
Map, harness, ship. In that order.
We do not start by rewriting. We start by proving what must not break.
02
Harness
Pin down the behavior.
Critical workflows captured. API contract snapshots. Golden tests for the boundaries that matter. A test that fails loudly is the deliverable, not a green CI run that lied.
Output:A test suite that owns the behavior, not the implementation.
03
Ship
Migrate, incrementally.
Bounded modernization increments sized to one module, route, workflow, or report. Each ships behind a parity check. You can stop at any time and what is shipped continues to work.
Output:Verified increments with rollback notes and evidence.
How a Modernization Preflight runs
Three weeks to the first verified increment. Then the same cadence on every tranche after.
- Week 1ReadWe sit with your team and read the code. Stack detection, repo summary, dependency age. No commits, no PRs. Notes only.
- Week 1 to 2MapModule, service, route, and API inventory. Dependency risk. Dead code candidates. Migration blockers. We agree on the boundary of the first increment.
- Week 2Capture behaviorCritical workflows captured. API contract snapshots taken. The safety harness starter goes green on the existing system before anything moves.
- Week 3First proof PROne bounded modernization increment shipped behind a parity check. Human-reviewed, with rationale, rollback notes, and verification evidence.
- OngoingTranchesSame cadence, smaller blast radius each time. The harness grows. The legacy shrinks. Stop at any time and what is shipped continues to work.
Proof protocol
The stack changes. The safety protocol does not.
Grayhaven works across legacy frontend, .NET, Java, Rails, WCF, spreadsheet, and workflow systems. We do not start by choosing a replacement framework. We start by proving what the current system does.
Every engagement follows the same sequence, regardless of stack.
- 01Map the system.Inventory modules, routes, services, dependencies, workflows, integrations, and migration blockers.
- 02Capture behavior.Turn critical workflows, API contracts, side effects, reports, and edge cases into executable evidence.
- 03Install the harness.Create tests, snapshots, fixtures, or parity checks that prove the existing system before anything moves.
- 04Ship one bounded increment.Modernize one route, workflow, module, service, report, or integration surface at a time.
- 05Verify parity.Show what changed, what did not, how rollback works, and what can safely move next.
Public specimen 001
AngularJS 1.8.3 Preflight
The first public system we used to show the protocol end to end: system map, behavior map, harness starter, migration sequence, first proof increment, and executive memo. The point is not Angular. The point is the artifact chain.
Download the sample Preflight23 pages·290 KB·Public source·No email required
Common modernization patterns
What Grayhaven engagements look like across the legacy lanes we work in.
These examples show the shape and verification posture of the work. They are anonymized composites, not customer case studies.
FrontendPE-backed vertical SaaS
AngularJS dashboard to React, behavior preserved.
Old AngularJS admin dashboard with weak test coverage. Behavior captured against a Playwright harness before any line of React was written.
3 wk
to verified harness
Parity-gated
every shipped increment
AngularJS → React
with parity check
.NETRegulated healthcare software
.NET Framework service stabilized before migration began.
Legacy ASP.NET MVC + WCF surface mapped, dependency risk scored, and API contract snapshots installed in CI before the first service was touched.
All agreed
critical workflows covered
Contract
snapshots in CI
.NET Framework → .NET 8
incremental
RailsMid-market B2B SaaS
Rails monolith made safely changeable.
Test-poor Rails 4 monolith with hidden business rules. Golden-path coverage installed before any service was extracted. Tranches sized to one workflow at a time.
One workflow
per tranche
Rollback
evidence per release
Rails 4 → Rails 7
behind harness
Data & workflowOperations team
Spreadsheet-driven reporting moved into a typed service.
Excel and VBA workflow with embedded business rules. Behavior captured as fixtures, ported to a typed service, and verified with before-and-after output comparison.
Auditable
behavior diff
Fixtures
from production traces
Excel/VBA → typed service
with tests
Java & SpringEnterprise platform team
Spring monolith mapped, harness installed, modules modernized in turn.
Spring 4 monolith with unclear service boundaries. Module-level risk map produced, contract tests added at the boundaries, then modules modernized to Spring Boot 3 one at a time.
One module
per tranche
Verification
package per PR
Spring 4 → Spring Boot 3
incremental
.NETPE operating partner
WCF surface retired behind a REST facade.
Sunsetting WCF service kept callers stable behind a REST facade with contract snapshots. Migration tranches retired the legacy surface one route at a time.
Behavior
captured before change
Bounded
blast radius per tranche
WCF → REST
with snapshots
Pricing
Start with a Preflight. Stay on a retainer when the work compounds.
Migration tranches and full programs are scoped separately on the call. You always keep your code and your IP.
Modernization Preflight
Two to three weeks. Fixed deliverables.
From
$25,000
- Legacy system map: modules, services, routes, dependencies, blockers.
- Behavior map: critical workflows, API contracts, and side effects.
- Safety harness starter, green on the existing system, ready for CI.
- Migration plan with risk by module and a 30 / 60 / 90 day sequence.
- One bounded first-proof PR, human-reviewed, with rollback notes.
- Executive memo: what can move first, what to leave alone.
Book a Preflight
Larger or regulated systems are scoped on a call. Migration tranches are priced separately.
Maintenance Retainer
Ongoing. Monthly cadence, stop any time.
From
$15k/mo
- Test and harness maintenance as the codebase evolves.
- Monthly dependency risk and security review.
- Continued retirement of legacy surfaces on a known cadence.
- Additional migration work orders, scoped and verified.
- Code quality and architecture reviews against the harness.
- Production triage for issues that touch modernization work.
Talk about a retainer
Designed for systems already under harness. You keep your code and your IP; we keep the safe-change layer healthy.
Start small.
Book a modernization diagnostic. Leave with a first boundary, a risk map, and a recommended next step.
We are deliberately slow to take on engagements. If we are not the right fit, we will say so on the first call.
Contact
Show us the system your team cannot safely change.
We’ll tell you whether a Preflight makes sense, what boundary we would inspect first, and what the first verified increment should be. If we’re not the right team, we’ll say so.
Location
United States
Phone
(405) 320-8212
Hours
Monday - Friday
8:00 AM - 7:00 PM
8:00 AM - 7:00 PM