Inherited a Codebase? First Steps for New CTOs & Developers

You just got handed the keys to a codebase you didn't write.

Maybe you're a new CTO at a startup. Maybe your company acquired another. Maybe the agency that built your MVP disappeared. Maybe the previous developer left without documentation.

Whatever the reason, you're now responsible for code you don't understand, built by people you can't ask questions to, using decisions you weren't part of.

Here's how to make sense of it without losing your mind or breaking production.

The First 24 Hours

1. Don't Touch Anything Yet

Seriously. The urge to "fix" things is strong. Resist it.

You don't know what's load-bearing. That weird-looking function might be the only thing keeping the app running. That "unused" file might be called dynamically. That "obvious bug" might be an intentional workaround for a vendor issue.

First, understand. Then change.

2. Get Access to Everything

Make a list and start checking boxes:

• Source code repository (GitHub, GitLab, Bitbucket)
• Production environment (Vercel, AWS, GCP, Heroku)
• Database access (read-only first!)
• Third-party services (Stripe, Auth0, SendGrid, etc.)
• Domain registrar and DNS
• Monitoring and logging (if any exist)
• CI/CD pipelines
• Documentation (ha, if it exists)

3. Verify You Can Deploy

Before understanding the code, verify the deployment pipeline works:

1. Can you pull the latest code?
2. Can you run it locally?
3. Can you deploy to a staging environment?
4. Do you have rollback capability?

If any of these are broken, fix them first. You can't safely change code you can't safely deploy.

The First Week: Mapping the Territory

Run an Automated Audit

The fastest way to understand an inherited codebase is an automated analysis. In minutes, you'll see:

• System architecture map (what connects to what)
• Security issues (exposed secrets, vulnerabilities)
• Dependency inventory (what's outdated, what's risky)
• Technical debt indicators (code complexity, test coverage)
• Framework and language detection

Identify the Critical Paths

Not all code is equally important. Find the paths that matter most:

Revenue paths:

• User signup and authentication
• Payment processing
• Core feature that users pay for

Data paths:

• Where does user data enter the system?
• Where is it stored?
• Who can access it?

Failure points:

• What happens if the database is unreachable?
• What happens if a third-party API goes down?
• Where are there no error handling?

Draw the Dependency Map

Understand what your system relies on:

Check for Secrets

Inherited codebases often have exposed secrets: credentials committed by developers who didn't know better or were "just testing."

Search for:

• .env files in the repository
• Hardcoded API keys in config files
• Database connection strings with credentials
• AWS access keys (strings starting with AKIA)

If you find any, rotate them immediately. You don't know who else has access to this repository's history. See our detailed guide on how to find exposed secrets in GitHub.

The First Month: Understanding Decisions

Read the Git History

The git history tells you more than the code itself:

# See who wrote what
git shortlog -sn

# See recent activity
git log --oneline -50

# See changes to a specific file
git log -p path/to/important/file.js

Look for:

• Who were the main contributors?
• When was the last commit?
• Are there abandoned branches with half-finished features?
• Are there revert commits? (Signs of "fixes" that broke things)

Find the Tribal Knowledge

Someone knows how this system works. Find them:

• Previous developers (if reachable)
• Customer support (they know what breaks)
• Power users (they know the workarounds)
• The person who handles production incidents

Get 30 minutes with each. Ask:

• "What's the scariest part of this system?"
• "What breaks most often?"
• "What do you wish worked differently?"
• "What should I absolutely not touch?"

Document As You Learn

You're going to forget what you learned. Write it down:

• Create a docs/ folder if one doesn't exist
• Document every "aha" moment
• Map out every gotcha and workaround
• Note which documentation is wrong (there will be some)

Future you (and future team members) will thank you.

Red Flags to Watch For

No Tests

Zero tests means zero safety net. Every change is a risk. Prioritize adding tests to critical paths before making changes.

One Giant File

A 5,000-line file is a sign that nobody knew where to put things. It's also a sign that refactoring will be painful and risky.

Dead Code Everywhere

Commented-out functions. Unused imports. Files that aren't referenced anywhere. These add cognitive load and hide the real logic.

"Temporary" Solutions That Aren't

Look for comments like:

• "TODO: fix this later"
• "HACK: this shouldn't work but it does"
• "TEMPORARY: remove after launch"

If they're more than a month old, they're permanent.

Outdated Dependencies

Check the lock file dates. Dependencies that haven't been updated in 2+ years probably have known vulnerabilities. But don't update them all at once. That's how you break things.

No Environment Separation

If the same credentials work for development and production, you have a serious risk. One wrong command could delete production data.

What Not to Do

Don't Rewrite Everything

The "rewrite from scratch" urge is strong but almost always wrong. The existing code, ugly as it may be, handles edge cases you don't know about. Rewrites take 3x longer than estimated and introduce new bugs.

Don't Refactor Without Tests

If there are no tests, add them before refactoring. Otherwise, you won't know if your "improvements" broke something.

Don't Remove "Dead" Code Without Verification

That "unused" function might be called dynamically. That "old" endpoint might be used by a mobile app you didn't know existed. Verify before deleting.

Don't Blame the Previous Developers

You don't know their constraints. Maybe they had no time. Maybe requirements changed constantly. Maybe they were learning as they built. Focus on improving, not judging.

Building a Remediation Plan

Once you understand the codebase, create a prioritized plan:

Priority 1: Security (This Week)

• Rotate any exposed credentials
• Patch critical vulnerabilities
• Enable basic monitoring if none exists
• Verify backup and restore procedures

Priority 2: Stability (This Month)

• Add error tracking (Sentry, etc.)
• Add basic tests to critical paths
• Document the deployment process
• Create a staging environment if none exists

Priority 3: Maintainability (This Quarter)

• Update critical dependencies
• Refactor the worst pain points
• Improve test coverage incrementally
• Consolidate duplicate code

Priority 4: Enhancement (Ongoing)

• Add features
• Improve performance
• Pay down technical debt
• Modernize architecture

When to Ask for Help

Some situations need outside expertise:

• Security breach suspected: Get a professional incident response team
• Compliance requirements: Get legal and compliance review
• Critical decisions: Get a second opinion before major changes
• Team scaling: Get advice on architecture before hiring

Frequently Asked Questions

How long until I'll fully understand this codebase?

For a typical startup codebase, expect 2-4 weeks to understand the main flows, 2-3 months to know where most things are, and 6+ months before you feel truly comfortable.

Should I upgrade all the dependencies?

No. Upgrade incrementally, starting with security-critical packages. Test thoroughly between each upgrade. Batch upgrading causes cascading breakage.

The previous developer is unreachable. Now what?

You have the git history and the running system. Use automated analysis tools to map the architecture. Document as you discover. Accept that some decisions will forever be mysteries.

How do I explain the technical debt to non-technical stakeholders?

Use business language: "We can add features, but each one has a higher risk of breaking something else. Investing time now in stability means faster, safer development later." For investor conversations, see our guide on technical due diligence.

Inheriting a codebase is overwhelming. But it's also an opportunity. You get to understand a system from the outside in, see its weaknesses clearly, and improve it systematically.

The developers who came before you did the best they could with what they had. Your job isn't to judge their work. It's to take it further.

Start by understanding what you have. Get a complete architecture map and health assessment in minutes.

Related reading:

• What Is Technical Debt?: Understanding the cost of shortcuts you inherited
• Code Audit Checklist: Systematic review for inherited codebases
• How to Find Exposed Secrets in Your GitHub Repo: First security check for any inherited code