What a technical due diligence actually looks for and what it usually finds

TL;DR: Most founders hear "technical due diligence" and assume it is something that happens to them during a raise. Those who come out of it well treat it as something worth doing themselves first. This post walks through what an assessment actually examines, the three findings that come up most often across real engagements and what a CTO or founder can check before anyone external looks.

Most founders picture a version of technical due diligence where an investor sends someone technical to look at the codebase, that person finds something alarming, and the deal either collapses or the valuation gets renegotiated downward.

That version happens, but the more common version is subtler and in some ways more expensive. The assessment surfaces findings that were already known internally, had been on the to-do list for months and would have been significantly cheaper to address before a raise than during one.

Technical due diligence has become standard practice for most private investors backing digital startups, and the scrutiny is not getting lighter.

 The founders who navigate it well are almost always the ones who understood what it was looking for before it started.

What an assessment actually examines

Technical due diligence is not a code quality competition. Nobody reviewing a codebase before an investment is grading the abstractions. They are trying to work out what it will cost to own the system and how badly it can go wrong after the money changes hands.

That reframing matters because it changes what the assessment is actually measuring. The six areas it covers in practice are these.

Architecture and whether it supports the next order of magnitude. Can the system handle 10x current load? Is the architecture flexible enough to support the product roadmap the pitch deck describes, or does it have structural constraints that would require a significant rebuild before that roadmap is achievable? This is not about whether the architecture is elegant. It is about whether it is a ceiling.

Test coverage and what its absence means for release confidence. Not whether tests exist, but whether the test suite gives the team genuine confidence that a change to one part of the system will not break something unexpected in another. A codebase with unit tests covering business logic but no integration tests covering how components interact will pass a superficial check and fail a serious one. The question an assessor is asking is whether the team can ship with confidence or whether every release is a calculated risk.

Deployment and whether one person is a single point of failure. This is the finding that surprises founders most often. The deployment process works. The team ships regularly. But the process lives in one engineer's head, or on one engineer's laptop, and has never been documented or tested by anyone else. That engineer is the single point of failure for every release. An investor funding growth wants to know that the team can scale without that dependency, and most cannot answer the question clearly when it is first asked.

Dependency and security posture. Are there third-party libraries or integrations running on deprecated versions? Are there known vulnerabilities in the dependency tree that have not been addressed? Is the IP ownership of the codebase clean, or are there components built by contractors whose assignment was never formalised? Any of these can become a legal or operational problem after a funding event. Assessors look for them specifically.

Documentation and key-person risk. How much of the operational knowledge of the system lives in the codebase and how much lives in the heads of one or two engineers? A team where the departure of one person would leave the next engineer doing archaeology for three months is carrying key-person risk that an investor prices into the deal. This is true regardless of how well-written the code is.

Development process and team capability. How does the team make technical decisions? Is there a clear process for code review, for handling incidents, for managing technical debt? A team that makes decisions through informal consensus will struggle to adapt under the pressures of post-investment growth. Assessors are looking for signals of engineering maturity not just engineering output.

The three findings that come up most often

Across the engagements we have run, three findings appear consistently enough that a founder or CTO can almost always find at least one of them before an external reviewer does.

Finding 1: The deployment that depends on a person, not a process

The deployment process works in practice. It has worked for two years. But it has never been written down in a way that someone who did not build it could follow. There is a developer, usually one of the founders or the first senior engineer, who runs every significant release because they are the only person who knows the sequence that avoids the things that break.

This tends to be a process gap rather than a reflection of the codebase itself, and it is one of the most common findings in assessments because it accumulates naturally in teams that are focused on shipping rather than on documenting how they ship. The fix is usually a week of work to write it down and test it. The cost of having it surfaced by an investor's reviewer rather than finding it yourself is a renegotiation conversation that did not need to happen.

Finding 2: Test coverage that looks adequate until it is tested

Most teams have tests. Most teams do not have a test suite that gives genuine release confidence across the whole system. The common gap is between unit test coverage, which is often reasonable, and integration test coverage, which is often absent or partial. The result is a system where a change to one service can have downstream effects on two others that the tests do not catch, and where the team knows this and manages around it rather than addressing it.

An assessor looking at test coverage will ask not just what percentage of lines are covered but what the team's actual confidence level is when shipping to production. The honest answer to that question is usually more informative than any coverage metric.

Finding 3: IP and dependency hygiene that was deferred

The codebase includes components built by contractors over the past two years. The IP assignment was never formalised in writing. Or there are third-party libraries in the dependency tree running on versions that stopped receiving security patches twelve months ago, and nobody has made time to update them because nothing has broken yet. Sometimes both.

These are largely administrative rather than engineering failures, and they are fixable in weeks. But they are the kind of thing that an investor's legal team flags immediately, and that creates friction in a deal at exactly the moment when friction is most expensive.

What a CTO or founder can check before anyone external looks

The self-assessment does not need to be exhaustive to be useful. These four checks will surface the findings most likely to affect a raise.

Run a deployment drill. Ask someone who was not involved in building the deployment process to deploy to a staging environment using only what is documented. If they cannot do it without asking questions, the documentation is insufficient. Fix it before anyone external asks the same question.

Ask the team honestly about release confidence. Not "do we have tests" but "if we shipped the next release tonight, how confident are we that nothing unexpected would break?" If the honest answer is "fairly confident, mostly" rather than "very confident, here is why," that is the gap to close.

Audit the dependency tree. Run a dependency audit against known vulnerability databases. Address anything flagged as high severity. Check that the versions of key libraries and frameworks the codebase depends on are currently supported. This is a half-day job for a senior engineer and eliminates one of the most common assessment findings before it can be raised.

Check IP ownership for all contracted work. If any part of the codebase was built by contractors, confirm in writing that the IP was assigned to the company. If it was not, get it done. This is a legal formality that becomes a legal problem if it is missing when a deal is being structured.

You can read more about how we approach structured codebase assessments in our post on what we found in the codebase and what it was costing them, and see how we have worked with high-growth platforms like Pitchero on long-term technical delivery across a codebase serving over five million users.

Frequently asked questions

What is technical due diligence for a UK startup? Technical due diligence is a structured assessment of a startup's technology, covering the codebase, architecture, infrastructure, security posture, development process and team capability. It is conducted before an investor commits capital and examines whether the product is built on a foundation that can support the growth the business is projecting. 

What do investors look for in technical due diligence? Investors are not looking for a perfect codebase. They are looking for evidence that the system can be owned, maintained and scaled after the investment. The six areas typically examined are architecture and scalability, test coverage and release confidence, deployment process and single-point-of-failure risk, dependency and security posture, documentation and key-person risk and development process and team capability.

What are the most common findings in a technical due diligence for a startup?

Three findings appear most consistently. A deployment process that depends on a specific person rather than a documented process. Test coverage that looks adequate in summary but does not provide genuine release confidence across the whole system. IP and dependency hygiene issues, typically contractor work without formal IP assignment or third-party libraries running on unsupported versions.

How should a UK startup prepare for technical due diligence? The most effective preparation treats it as something to do proactively rather than reactively. Four checks cover most of the common findings: run a deployment drill using only documentation, ask the team honestly about release confidence, audit the dependency tree for known vulnerabilities and check IP ownership for all contracted work. Each of these is fixable in days or weeks. Surfacing them through an investor's reviewer rather than finding them yourself creates friction at exactly the wrong moment.

When should a UK startup do a self-assessment before a technical due diligence? As early as possible and certainly before a raise is underway. The most expensive time to discover a significant finding is during active deal negotiations. A self-assessment three to six months before a planned raise gives enough time to address most findings without time pressure. For founders planning a 2027 raise, starting that process in October or November 2026 is the right window.

How Aecor helps

We run structured technical assessments for startups and scale-ups at two stages: before a raise, as a self-assessment that surfaces findings while there is still time to address them, and as part of an onboarding process when we begin working with an existing codebase. The assessment follows the same structure as what an investor's technical reviewer would examine, which means the findings and the remediation are directly relevant to what a due diligence process will look at.

If you are planning a raise in 2027 and want to understand where your codebase stands before anyone external looks, a free 60-minute technical discovery call is a good place to start.

Book your free Technical Discovery Call