The first 90 days: a CTO's guide to inheriting a messy codebase

The email arrives on a Sunday evening: “Congratulations! We’re excited to have you join as our CTO. Quick heads up, the previous technical lead left abruptly, and there might be a few technical challenges to sort out.”

Translation: You’re about to inherit a technical disaster.

I’ve been in this situation more times than I care to count over my 20-year career, and I’ve coached dozens of CTOs through similar scenarios. That “few technical challenges” usually means you’re walking into a codebase that’s held together by prayers, duct tape, and one developer who’s afraid to take vacation because everything might break.

Here’s the brutal truth: Your first 90 days will determine whether you can turn this ship around or whether you’ll be the next CTO making a hasty exit.

This guide is your battle-tested framework for those critical first three months. It’s not about perfection. It’s about survival, quick wins, and building the foundation for long-term success. This framework builds on general CTO onboarding principles, adapted specifically for technical chaos scenarios.

The Reality of Inheriting Technical Chaos

Let me paint you a picture from my consulting work. Last year, I helped a new CTO who joined a “fast-growing” fintech startup. The founder proudly showed off their 50,000+ lines of code and boasted about their development velocity.

Within a week, the new CTO discovered:

• No testing framework (zero automated tests)
• Database credentials hardcoded in 47 different files
• A “temporary” fix from 2019 that handled 80% of their transactions
• Two different authentication systems running in parallel
• Documentation that hadn’t been updated since the company pivoted 18 months earlier

Sound familiar? This isn’t an extreme case. It’s typical.

Why Codebases Become Disasters

After cleaning up dozens of messy codebases, I’ve identified the common patterns:

The Pressure Cooker Effect: Startups prioritize speed over sustainability. Every feature is “urgent,” every fix is “temporary,” and technical debt accumulates faster than credit card interest.

The Knowledge Hoarding Problem: Critical information lives in one person’s head. When they leave (or get hit by a bus), their knowledge leaves with them.

The “We’ll Fix It Later” Syndrome: Later never comes. Technical debt compounds until the system becomes unmaintainable.

The Outsourcing Roulette: Multiple development agencies have contributed code without coordination, creating a Frankenstein’s monster of different patterns and approaches.

The New CTO’s Impossible Mission

You’re expected to:

• Keep the existing system running
• Deliver new features at the same pace
• Improve code quality and reduce bugs
• Scale the team and architecture
• Do all of this while learning a completely new codebase

It’s like being asked to rebuild a plane while flying it, in a thunderstorm, with passengers complaining about the turbulence.

Days 1-30 - The Assessment Phase

Your first month is about understanding what you’re dealing with. Resist the urge to fix everything immediately. Bad decisions made quickly will haunt you for months.

Week 1: The System Archaeology

Day 1-2: Get the System Running Locally

This sounds basic, but it’s often harder than it should be. I’ve seen new CTOs spend their entire first week just getting the development environment working.

What to document:

• How many steps does it take to run the system locally?
• What assumptions are made about the developer’s environment?
• What breaks, and what workarounds are needed?

Red Flag Indicators:

• Setup takes more than 2 hours
• Requires specific versions of tools that aren’t documented
• Depends on external services that might not be accessible
• Needs data or configurations that aren’t in version control

Day 3-5: Map the System Architecture

Create a high-level diagram of how the system works. Don’t worry about being perfect. You’re creating a mental model.

Key questions:

• What are the main components and how do they communicate?
• Where is data stored and how is it accessed?
• What external services are integrated?
• How does deployment work?

I use a simple format: boxes for services, arrows for data flow, and different colors for different types of components (databases, APIs, UIs, etc.).

Day 6-7: Interview the Team

Talk to everyone who touches the codebase:

• What parts of the system do they understand best?
• What are their biggest pain points?
• What are they afraid to touch?
• What would they fix first if they could?

Week 2: The Technical Deep Dive

Code Quality Assessment

Run automated tools to get objective metrics:

• Code coverage (if tests exist)
• Code complexity metrics
• Security vulnerability scans
• Dependency analysis for outdated packages

But remember: metrics don’t tell the whole story. I’ve seen codebases with 90% test coverage that were still unmaintainable because the tests were testing the wrong things.

The Critical Path Analysis

Identify the most important user journeys and trace them through the code:

• User registration and login
• Core product functionality
• Payment processing (if applicable)
• Data import/export

Map out what happens when these processes fail. Often, you’ll find that critical business functions depend on the most fragile parts of the system.

The Bus Factor Audit

For each critical component, ask: “What happens if the person who understands this best leaves tomorrow?”

I call this the “lottery ticket test.” If your lead developer wins the lottery and quits, what parts of your business stop working?

Week 3: The Production Reality Check

Monitor Production Systems

Get access to:

• Error logs and monitoring dashboards
• Performance metrics
• Database performance data
• User analytics and behavior data

The Failure Mode Investigation

Ask these questions:

• What has broken in the last 6 months?
• How long did it take to fix?
• What was the business impact?
• How was the problem detected?

I once worked with a company that didn’t realize their payment processing was failing 15% of the time because they weren’t monitoring payment completion rates.

Customer Impact Assessment

Review support tickets and customer complaints:

• What technical issues are affecting users?
• How often do technical problems require manual intervention?
• What features do customers request most often?

Week 4: The Strategic Assessment

Technical Debt Categorization

Not all technical debt is created equal. I classify it into three categories (learn more about systematic approaches to technical debt prioritization and management):

1. Critical Debt: Issues that threaten system stability or security
2. Productivity Debt: Issues that slow down development
3. Feature Debt: Missing functionality that limits business growth

Scalability Bottlenecks

Identify what will break first as you grow:

• Database performance limits
• Infrastructure capacity constraints
• Third-party service rate limits
• Architecture decisions that don’t scale

Team Capability Assessment

Honestly evaluate your team’s capabilities:

• What skills do you have vs. what skills do you need?
• Who are your strongest contributors?
• What knowledge gaps exist?
• How is the team’s morale and confidence?

Days 31-60 - Quick Wins and Stabilization

Month two is about building credibility through visible improvements while preparing for bigger changes.

The Quick Wins Strategy

You need early victories to build trust with the business and confidence with your team. Focus on high-impact, low-risk improvements.

Quick Win #1: Improve Observability

Before you can fix problems, you need to see them. Implement:

• Basic error monitoring and alerting
• Performance monitoring for critical paths
• Simple dashboards for business metrics
• Automated deployment success/failure notifications

I’ve seen this single change reduce time-to-resolution for production issues by 70%.

Quick Win #2: Stabilize the Development Process

Small process improvements with big impact:

• Consistent code formatting (Prettier, ESLint, etc.)
• Automated dependency updates
• Improved local development documentation
• Basic CI/CD improvements

Quick Win #3: Address the Most Painful Manual Processes

Every messy codebase has manual processes that waste time:

• Manual deployment steps
• Manual data migrations
• Manual testing procedures
• Manual monitoring tasks

Automate the most painful one first.

The Stabilization Framework

Create a Bug Triage System

Classify bugs into categories:

• P0: System down or data loss
• P1: Major functionality broken
• P2: Minor functionality issues
• P3: Cosmetic issues

Establish clear response time expectations for each priority level.

Implement Code Review Standards

If code reviews aren’t happening, start them immediately. Focus on:

• Security implications
• Performance impact
• Maintainability concerns
• Knowledge sharing

Begin Documentation Recovery

Start with the most critical missing documentation:

• How to deploy the system
• How to investigate production issues
• Architecture decision records for major components
• Onboarding guide for new developers

Team Building and Communication

Weekly Technical Debt Reviews

Start a weekly 30-minute meeting focused on technical debt:

• What technical issues slowed us down this week?
• What quick improvements could we make?
• What technical risks are we accumulating?

Establish Clear Communication Channels

Create structured communication:

• Daily standups focused on blockers and dependencies
• Weekly team retros to identify process improvements
• Bi-weekly architecture discussions for bigger decisions

Begin Knowledge Transfer

Start documenting tribal knowledge:

• Create runbooks for common production issues
• Record video walkthroughs of complex system components
• Pair program to distribute critical knowledge

Days 61-90 - Building the Foundation for Long-term Success

Your final month is about establishing the foundation for sustainable technical improvement.

The Long-term Technical Strategy

Create Your Technical Vision

Develop a 12-18 month technical roadmap that balances:

• Business feature requirements
• Technical debt reduction
• Infrastructure improvements
• Team scaling needs

Don’t make this a perfect plan. Make it a directional guide that you can adjust based on learning.

Establish Architecture Principles

Define your technical philosophy:

• How do you balance speed vs. quality?
• What technologies will you standardize on?
• How do you make build-vs-buy decisions?
• What security standards will you maintain?

Design Your Refactoring Strategy

You can’t rewrite everything, so prioritize:

1. Safety First: Address security vulnerabilities and stability issues
2. Productivity Second: Fix issues that slow down development
3. Performance Third: Address scalability and performance problems
4. Features Last: Add new functionality on a stable foundation

Team Development and Hiring Strategy

Assess Your Hiring Needs

Based on your first 60 days, you should know:

• What skill gaps exist in your team?
• What roles do you need to fill first?
• What kind of candidates will succeed in your environment?
• How quickly do you need to hire?

Create a Technical Interview Process

Design interviews that test for your specific needs:

• Can they work with legacy code?
• Do they understand your technology stack?
• Can they balance speed with quality?
• Do they fit your team culture?

Develop Your Current Team

Identify growth opportunities for existing team members:

• Who can take on more leadership responsibilities?
• What training would help team members be more effective?
• How can you create career growth paths?

Establishing Sustainable Practices

Implement Gradual Quality Improvements

Don’t try to fix everything at once. Instead:

• Add tests to critical paths as you work on them
• Refactor components when you need to modify them
• Improve documentation when you learn something new
• Automate processes when manual work becomes painful

Create Technical Debt Management Process

Establish a system for managing technical debt:

• Regular technical debt assessment and prioritization
• Allocation of development time for improvements (I recommend 20-30%)
• Clear criteria for when to refactor vs. rewrite
• Communication framework for explaining technical work to business stakeholders

Build Relationships with Business Stakeholders

Your success depends on business understanding and support:

• Regular updates on technical improvements and their business impact
• Clear communication about technical risks and constraints
• Collaborative planning that balances business and technical needs
• Education about the importance of technical investment

Common Pitfalls and How to Avoid Them

After coaching dozens of CTOs through this process, I’ve seen the same mistakes repeatedly:

Pitfall #1: The “Rewrite Everything” Trap

The Mistake: Deciding the codebase is so bad that you need to start over.

Why It’s Tempting: Rewriting feels clean and gives you complete control.

Why It’s Dangerous: Rewrites take 2-3x longer than expected, business features are delayed, and you often recreate the same problems in new code.

Better Approach: Incremental improvement and strategic refactoring. Ship improvements regularly rather than betting everything on a big rewrite.

Pitfall #2: The “Perfect Process” Obsession

The Mistake: Implementing comprehensive processes and tools before addressing immediate problems.

Why It’s Tempting: Processes feel like progress and give you a sense of control.

Why It’s Dangerous: Overhead without immediate value frustrates teams and delays real improvements.

Better Approach: Implement minimal viable processes that solve actual pain points, then iterate.

Pitfall #3: The “Technical Ivory Tower” Problem

The Mistake: Making technical decisions in isolation without considering business impact.

Why It’s Tempting: Pure technical decisions feel more objective and easier to reason about.

Why It’s Dangerous: Solutions that don’t align with business needs get deprioritized or abandoned.

Better Approach: Frame all technical work in terms of business value and risk reduction.

Pitfall #4: The “Hero Complex” Syndrome

The Mistake: Trying to solve all technical problems personally.

Why It’s Tempting: You’re the expert, and fixing things yourself feels faster.

Why It’s Dangerous: Creates knowledge bottlenecks and doesn’t scale.

Better Approach: Focus on enabling your team to solve problems rather than solving them yourself.

Measuring Success in Your First 90 Days

How do you know if you’re succeeding? Here are the metrics that matter:

Technical Metrics

System Stability:

• Reduction in production incidents
• Faster incident resolution times
• Fewer emergency deployments

Development Velocity:

• More consistent sprint completion
• Reduced time from code to production
• Fewer bugs found in production

Code Quality:

• Increased test coverage (for new code)
• Reduced complexity in critical components
• Better code review participation

Team Metrics

Developer Experience:

• Faster onboarding for new team members
• Reduced time to get development environment working
• Higher developer satisfaction scores

Knowledge Distribution:

• More people can handle production issues
• Better documentation coverage
• Reduced single points of failure

Business Metrics

Feature Delivery:

• More predictable delivery timelines
• Fewer feature rollbacks due to technical issues
• Better business-technical communication

Risk Reduction:

• Identified and documented technical risks
• Clear plans for addressing critical technical debt
• Improved security posture

Beyond the First 90 Days - Setting Up for Long-term Success

Your first 90 days are just the beginning. Here’s how to set yourself up for continued success:

Build a Culture of Continuous Improvement

Regular Technical Health Checks: Schedule quarterly assessments of your technical landscape:

• What new technical debt have we accumulated?
• What assumptions have been proven wrong?
• What new risks have emerged?
• What improvements have had the biggest impact?

Invest in Learning: Create systems for staying current:

• Regular tech talks and knowledge sharing sessions
• Conference attendance and training budgets
• Experimentation time for exploring new technologies
• Post-mortem processes that focus on learning

Scale Your Impact

Develop Other Technical Leaders: Your success depends on developing leadership in others:

• Identify and mentor high-potential team members
• Create opportunities for technical leadership
• Delegate meaningful technical decisions
• Build systems that don’t depend on your personal involvement

Create Scalable Processes: Design processes that work as you grow:

• Automated quality checks that don’t require manual intervention
• Self-service tools for common developer tasks
• Documentation systems that stay current
• Decision-making frameworks that don’t bottleneck on you

Maintain Strategic Perspective

Balance Technical and Business Needs: Never lose sight of the business context:

• Regular check-ins with business stakeholders
• Clear communication about technical constraints and possibilities
• Involvement in product and business strategy discussions
• Translation of business needs into technical requirements

Conclusion: Your Journey from Chaos to Control

Inheriting a messy codebase isn’t a career death sentence. It’s an opportunity to make a significant impact. Some of the most successful CTOs I know built their reputations by turning around technical disasters.

The key is approaching it systematically:

Days 1-30: Understand what you’re dealing with Days 31-60: Build credibility through quick wins Days 61-90: Establish foundations for long-term success

Remember:

• You can’t fix everything immediately, but you can fix something every week
• Perfect is the enemy of good. Focus on progress, not perfection
• Your team’s success is your success. Invest in their capabilities
• Communication with business stakeholders is as important as technical work
• Every disaster codebase has value embedded in it. Respect what exists while improving it

Your Action Plan

Here’s your checklist for getting started:

Week 1:

• Get the system running locally and document the process
• Create a high-level architecture diagram
• Interview every team member about their pain points

Week 2:

• Run code quality analysis tools
• Map critical user journeys through the code
• Identify single points of failure

Week 3:

• Get access to production monitoring and logs
• Review recent production incidents
• Analyze customer support tickets for technical issues

Week 4:

• Categorize technical debt by impact and effort
• Assess team capabilities and hiring needs
• Create your first 90-day improvement plan

The companies I’ve worked with that successfully turned around their technical situations all had one thing in common: they started with a clear assessment, made incremental improvements consistently, and maintained focus on business value.

You’ve got this. The fact that you’re reading this guide means you’re taking a thoughtful approach to a challenging situation. That’s exactly the mindset that leads to success.

I’ve helped dozens of CTOs navigate inherited technical chaos over my 20-year career. If you’re facing this challenge and want a structured approach tailored to your specific situation, let’s talk about how I can help you build a plan that works.