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Legacy Stabilization

Fix revenue-critical paths fast. Untangle old code, reduce risk, and keep the business running while you figure out what's next.

You inherited a codebase. Maybe you acquired a company. Maybe the original developer left. Maybe it's your own code from three years ago (we don't judge). Either way, it's keeping the lights on—but touching it feels dangerous.

Legacy stabilization is about making old code safe to work with again. Not a rewrite. Not a migration. Just enough changes to stop the bleeding and let you move forward.

The real problem with legacy code

It's rarely about the technology being "old." We've seen ancient PHP codebases that run like clockwork and modern TypeScript apps that are unmaintainable nightmares. The problem is usually:

Why Legacy Code Becomes RiskyNo TestsChanges break thingsFear of refactoring"If it works, don't touch it"Lost ContextOriginal devs are goneNo documentationMagic numbers everywhereImplicit DependenciesHidden database triggersCron jobs nobody knowsUndocumented APIsOutdated DepsSecurity vulnerabilitiesBreaking changes pile up"We can't upgrade Node"After StabilizationCritical paths tested • Dependencies documented • Safe to modify • Clear upgrade pathMake changes without holding your breath

The good news? You don't need to fix everything. You need to fix the parts that matter.

What we actually do

1. Map the critical paths

First, we figure out what actually matters. In most legacy systems, 80% of the value comes from 20% of the code:

Critical Path AnalysisHIGHUser signup → Payment → First order12 files • 0% test coverage • Last modified 2021Any break = no revenueHIGHOrder fulfillment → Inventory → Shipping28 files • 15% test coverage • Last modified 2022Breaks = angry customersLOWAdmin dashboard → Reporting → Exports45 files • 0% test coverage • Last modified 2020Internal tool, workarounds existPriority: Fix #1 and #2 first. #3 can wait.

2. Add safety nets first

Before changing anything, we add tests around the critical paths. Not for coverage metrics—for confidence:

Safety Net TestsDocument existing behavior, bugs and all✓ Valid card → Purchase completesUser + Product + Valid paymentOrder createdNote: Tax calculation is wrong (known bug, documented)✓ Declined card → Fails gracefullyUser + Product + Declined cardNo orderUser sees clear error, no orphan dataThese tests don't fix bugs — they document what the code actually doesNow you can change code knowing you'll catch regressionsConfidence to refactor without fear

3. Document the weird stuff

Every legacy codebase has "magic" that nobody understands. We find it and document it:

Documenting Hidden BehaviorcalculateOrderTotal()Legacy pricing logicNow DocumentedHidden Business Rules:• Orders over $500 → free shipping (hardcoded)• VIP users → 10% off (hardcoded customer IDs)• Discount stacking order: percentage first, then fixedKnown Bugs (Now Features):• Rounding after discounts → ±$0.01 differences• "SUMMER2019" code still works (15% off)Full documentation: /docs/legacy/pricing-behavior.mdBefore"Don't touch this"After"Change carefully, test this"

4. Strangler fig for the scariest parts

When code is truly untouchable, we wrap it rather than modify it:

Strangler Fig PatternWrap risky code instead of modifying itOrderWrapper (Safety Rails)Feature FlagGradual rolloutNew CodeTested, modernLegacy Code (Untouched)+ Logging + Validation + Error alertingProcessedSafe either wayStart with small orders → expand gradually → eventually retire legacyZero downtime, reversible at any point

We don't advocate for rewrites

Full rewrites almost never work. They take longer than estimated, introduce new bugs, and often fail to capture the implicit business logic that's baked into the old code. Instead, we stabilize what exists and incrementally improve it.

The process

Legacy Stabilization ProcessWeek 1DiscoveryMap critical pathsIdentify risksInterview stakeholdersWeeks 2-3Safety NetsAdd critical path testsDocument behaviorSet up monitoringWeeks 4-5StabilizationFix urgent issuesWrap risky codeUpdate dependenciesWeek 6HandoffDocumentationRunbook creationKnowledge transfer

What you get

At the end of a legacy stabilization engagement:

  • Critical path documentation — Maps of what matters, what's risky, and what can be safely ignored
  • Test coverage where it counts — Not 100% coverage everywhere, but 100% coverage on the parts that could cost you money
  • Dependency updates — Security vulnerabilities patched, upgrade path documented
  • Monitoring & alerts — Visibility into the parts that used to be black boxes
  • Runbooks — Step-by-step guides for when things go wrong (because they will)
  • Confidence — The ability to make changes without wondering if you just broke production

This isn't about making it pretty

We're not here to refactor your code into something that wins architecture awards. We're here to make it safe to work with. Sometimes that means leaving ugly code ugly—but documented and tested.

The goal is simple: when something needs to change, you can change it without fear.

Pricing

Scoped engagements based on codebase complexity. We assess first, then quote.

Targeted Stabilization

For codebases where you know what's broken and need specific areas made safe to work with.

$6,000 fixed
  • Critical path mapping
  • Tests for revenue-critical flows
  • Dependency security updates
  • Basic documentation
  • Deployment improvements
  • Knowledge transfer session
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Recommended

Full Stabilization

For inherited codebases that need comprehensive work before your team can safely make changes.

$11,000–$15,000
  • Complete codebase audit
  • Comprehensive test coverage
  • Full dependency overhaul
  • Architecture documentation
  • Monitoring & alerting
  • CI/CD pipeline setup
  • Runbooks for common issues
  • Extended team training
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Frequently asked questions

This is actually our specialty. We use a combination of code archaeology, runtime analysis, and stakeholder interviews to piece together how things work. We document behavior as we discover it, including the 'bugs that are now features' that users depend on.
No. We work on live systems using techniques like strangler fig patterns and feature flags. Changes are rolled out gradually with monitoring. We never do big-bang deployments on legacy systems—that's how outages happen.
We've worked with PHP, Ruby, Python, Java, .NET, and more. Legacy stabilization is more about patterns and practices than specific languages. If it's something truly exotic, we'll let you know upfront.
Almost never. Rewrites take longer than expected, introduce new bugs, and often fail to capture the implicit business logic baked into the old code. We'll stabilize what exists and help you modernize incrementally. If a rewrite truly makes sense, we'll tell you—but it's rarely the answer.
We focus on revenue-critical paths and high-risk areas first. The checkout flow that processes payments? That gets tests before the admin dashboard that three people use. We'll map out the critical paths with you in week one.
Production readiness is about hardening a system that's fundamentally sound but needs polish—better monitoring, CI/CD, error handling. Legacy stabilization is about making scary, undocumented code safe to work with. Sometimes there's overlap, and we'll recommend the right approach for your situation.