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Taking over a codebase: a 30 day checklist

New team reviewing an unfamiliar codebase

Published on:

June 11, 2026

TAG:

PLATFORM ENGINEERING

BY:

Edgeless Team

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6 MIN READ

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Taking over a codebase is a common moment. A new hire, a change of agency or a company acquisition all produce the same task: understand a system quickly enough to change it without breaking it. The first month sets the tone. A structured inspection finds the risks and builds the confidence to ship.

Week one: get it running

The first goal is a working local environment. Follow the documentation, and write down every step that was missing or wrong. A codebase that cannot be run by a new person is a dependency on the people who already know it.

Deploy to a staging environment on day one if possible. A deployment that only one person can perform is the largest operational risk in most small teams. Doing it yourself while they watch turns a mystery into a process.

Read the tests, not the whole codebase. Tests describe the behavior the team considered important. The absence of tests around a module tells you where changes are risky, and the shape of the tests tells you what the authors expected to change.

Week two: map the system

Draw the system from the outside in. What are the entry points, what services exist, what data stores, what external integrations, what scheduled jobs. Keep the diagram rough and update it as you learn. The act of drawing exposes the parts nobody can explain.

Find the data. Where the production data lives, how it is backed up and who can restore it. Test a restore on a sample if the team allows it. A backup that has never been restored is a hope, and the first month is the right time to find out.

List the third party services and their owners. Payment, email, maps, analytics, hosting, certificates. Every one has an account, a renewal date and a person who can log in. Missing access to one of them can block a release for a day.

A local environment that runs from a clean checkout.
A deployment path you have executed yourself.
A diagram of services, data stores and integrations.
A restore test with a measured time.
Access to every third party account and the billing owner.
A list of scheduled jobs and what happens if one fails.

Week three: find the sharp edges

Look for the places where a change is likely to hurt. Code with no tests, logic duplicated across files, a dependency several major versions behind. Read the issue tracker and the incident history for the last year. Recurring problems point to a structural cause rather than bad luck.

Check the error tracking and the logs. A system that produces hundreds of ignored errors a day has lost the signal that would reveal a real problem. Fixing the noise is often the first useful contribution a new team can make.

Run a security pass on the basics. Dependencies with known vulnerabilities, secrets in the repository, admin routes without authentication, debug settings in production. None of these requires a full audit, and finding one early builds trust with the business.

Diagram of services and dependencies during a handover — Draw the system before changing it. The parts nobody can explain are the parts that will cause the next incident.

Week four: ship something small

Pick a small, visible change and take it all the way to production. A copy fix, a minor feature, a dependency update. The point is to exercise the whole path: branch, review, test, deploy, verify. The first release teaches more than another week of reading.

Document what you learned while it is fresh. Update the readme, add the missing steps and record the decisions that surprised you. That document is the beginning of the handover guide for the next person.

Agree on the first month of work with the business. A list of ten improvements ranked by risk and value, with the first two started. A new team that arrives with a plan is easier to trust than one that spends a quarter exploring.

Record the time each step took. Local setup, deployment, the first review and the first release. Those numbers become the baseline for onboarding the next person, and they show quickly whether the environment is improving or still depends on tribal knowledge.

Set a rule for changes to the plan. Any new urgent request should replace an item rather than being added on top. A first month with no capacity limit becomes a list of everything, and the important work is the first thing to slip.

People and knowledge

Find out who knows what. The person who understands the billing logic, the person who can restore the database, the person who knows why a workaround exists. Those names belong in the documentation, along with a plan to reduce the dependency.

Interview the outgoing team if they are still available. Ask what they would fix first, what they are afraid of and what they would not touch. A two hour conversation can save a month of discovery.

Write the answers down with names and dates. Memory of a handover fades quickly, and the next person will need the same context. A short page per system with the owner, the quirks and the known risks is enough to start.

Reduce the concentration deliberately. Pair on the risky tasks, record the walkthroughs and rotate the on call. A team that can operate a system without one person is more resilient than a team that has the smartest person on call.

Be honest about what you do not know. A new team that pretends to understand everything makes expensive assumptions. A short list of open questions, shared with the business, is a sign of competence rather than weakness.

A testing strategy you can start

You do not need to reach a coverage target in the first month. Add tests around the paths you are about to change and around the areas with a history of incidents. A small suite that covers the critical flow is more valuable than a large suite that tests getters.

Run the tests in the deployment pipeline, not only on a laptop. A test suite that is not enforced will drift. Start with the tests that already exist, fix the flaky ones and add one new test for every bug you fix.

Write down the environments and the data they use. A staging environment with production-like data catches problems that a demo database hides. If real data cannot be used, generate a representative set with the same shapes and edge cases.

The first ninety days

After the first month, shift from inspection to improvement. Pick the two highest risk items from the list and fix them with the team. The work should be visible to the business, not a private cleanup that nobody can evaluate.

Establish the routines that keep a codebase healthy: a release cadence, a dependency update schedule, an incident review and a quarterly look at the risk list. Those habits matter more than any single fix because they prevent the next round of decay.

Report progress in business terms. Releases per month, time to deploy, incidents, manual hours removed. A new team that can show those numbers earns the space to do the deeper work later.

The first month is for finding the risks and shipping one small change. Everything after that depends on both.
Edgeless Team

We take over codebases with a structured first month: environment, deployment, data, risks and a small release to production.

Explore software development

A handover is not complete when the access is transferred. It is complete when a new team can deploy, restore and change the system without calling the old one. The thirty day checklist is how that becomes true.

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Taking over a codebase: a 30 day checklist

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