What happens when VCs send engineers to review your codebase — the process, what they look for, common red flags, and how to prepare your team.
You’ve passed the partner meeting, the investment committee is interested, and then the email arrives: “We’d like to schedule a technical due diligence call with your CTO and engineering team.” For many founders, this is the moment they realize they haven’t thought carefully enough about technical debt, code quality, and architecture documentation. Technical due diligence doesn’t kill many deals — but it does kill some, and it changes the terms of most.
Understanding the technical due diligence process before you start fundraising gives you the preparation time to address the problems that would otherwise surface during the process.
Table of Contents
- What Technical Due Diligence Is and When It Happens
- Who Conducts Technical Diligence
- The Nine Areas VCs Evaluate
- Red Flags That Kill or Delay Deals
- How to Prepare Your Technical Stack Before Fundraising
- Managing the Technical Diligence Process
- Frequently Asked Questions
What Technical Due Diligence Is and When It Happens
Technical due diligence is the systematic review of a startup’s technology — its architecture, codebase, infrastructure, security practices, team capabilities, and development processes — conducted by investors or their advisors before closing an investment.
It typically happens after a term sheet is signed or after a verbal commitment is made at partner level — meaning you’ve already passed the investment decision in principle, and technical diligence is a confirmation process rather than a discovery process. A technical diligence finding that kills a deal is unusual; findings that reduce valuation, add conditions to closing, or require specific remediation before funds are released are more common.
At seed stage, technical diligence is often light or absent — the product and team are too early for deep code review to be meaningful. At Series A and beyond, particularly for enterprise software companies where the technology stack is a core asset, technical diligence is standard practice. Companies raising from specialist deep tech or AI funds should expect technical diligence at any stage where the technology thesis is central to the investment.
Who Conducts Technical Diligence
Technical diligence is conducted by one of three types of reviewers:
Internal VC engineers. Some larger funds have in-house technical partners — former CTOs or senior engineers — who conduct technical reviews. a16z has built an internal engineering team for this purpose. These reviewers are typically the most efficient because they understand both the investment context and the technical evaluation.
External advisors. Many mid-size funds engage technical advisors — experienced engineers, former CTOs, or academic experts in relevant domains — for specific deals. These advisors bring domain depth (if you’re an AI company, they may engage an ML specialist) but may be less attuned to the investment context.
Third-party technical due diligence firms. Specialized firms (Software Engineering due diligence firms, cybersecurity consultancies) conduct systematic reviews for a fee. This approach is most common for growth-stage companies where the codebase is large and the investment is significant.
The identity of the reviewer matters for preparation: internal VC engineers tend to focus on architecture and scalability, external domain advisors on technical differentiation and defensibility, and third-party firms on security and compliance.
The Nine Areas VCs Evaluate
1. Architecture and Scalability
Reviewers assess whether the system architecture can handle 10–100× growth without fundamental rebuilds. Monolithic architectures are not automatically red flags — many successful companies scale monoliths effectively — but reviewers want to understand whether scalability has been considered and where the current constraints are.
Key questions: What are the bottlenecks at 10× current load? What would need to be rebuilt to handle that load? Has the team run load tests?
2. Code Quality and Technical Debt
Reviewers assess the codebase’s maintainability, test coverage, documentation, and the ratio of feature development time to bug fixing. High technical debt isn’t disqualifying, but undisclosed technical debt — particularly debt that affects the reliability of core product functionality — is a red flag.
Key metrics: test coverage percentage, code review process, CI/CD pipeline presence, deployment frequency, mean time to recovery from incidents.
3. Technology Stack Choices
The specific languages, frameworks, and infrastructure choices matter less than the reasoning behind them. A well-reasoned choice of an unusual stack is fine; an unexplained choice of outdated technology that creates hiring difficulty is a concern.
Key question: Why did you choose this stack, and what would you choose differently now?
4. Security Practices
Security due diligence has intensified significantly in 2025–2026 following high-profile breaches at VC-backed companies. Reviewers look for: encryption at rest and in transit, secrets management (no hardcoded credentials), access controls and least-privilege principles, vulnerability scanning in the CI/CD pipeline, and penetration testing history.
For companies handling personal data — particularly healthcare, fintech, or HR tech — GDPR/HIPAA/SOC 2 compliance documentation is increasingly expected at Series A.
5. Infrastructure and DevOps
Cloud infrastructure setup, deployment processes, monitoring and alerting, and disaster recovery planning. Reviewers want to see that the production environment is stable, monitored, and recoverable — not that it’s sophisticated, but that it’s deliberate.
Key questions: What is your uptime over the past 12 months? How long does it take to deploy a change? What happens when your primary database fails?
6. Data Architecture and IP
Particularly relevant for AI and data-intensive companies. Reviewers assess: where data is stored and how it’s managed, data lineage and quality controls, training data provenance for ML models, and whether the company has genuine data assets or depends entirely on third-party data sources.
7. Intellectual Property
Confirmation that all code written by founders, employees, and contractors has been properly assigned to the company. Open source license compliance — particularly ensuring no GPL-contaminated code in commercial products. Freedom-to-operate in the context of any relevant patents.
8. Team Capabilities
Technical reviewers form views about the engineering team’s capabilities — not just from the codebase, but from conversations with technical leadership. Questions about technical decision-making, architecture tradeoffs, and future roadmap choices reveal engineering judgment in ways that code alone doesn’t.
9. Product-Market Alignment of Technical Choices
A subtle but important assessment: does the technical architecture reflect a clear understanding of what the product needs to do, or does it reflect academic preferences, premature optimization, or technical choices that don’t align with the business model? Enterprise software that can’t support multi-tenancy, consumer apps without mobile-first architecture, or data companies without data pipelines all signal misalignment.
Red Flags That Kill or Delay Deals
Most technical findings are manageable — they result in conditions or timeline adjustments rather than deal death. The findings that genuinely kill deals are:
Undisclosed IP ownership gaps. Code written before incorporation, contractor code without assignment agreements, or university IP claims that weren’t disclosed in the business due diligence. Discoverable IP problems after a term sheet is signed are serious because they suggest the founders weren’t fully transparent.
Fundamental architecture that can’t scale. A product built on architecture that would require a complete rewrite to handle 5× current load is not just technical debt — it’s a risk to the entire growth thesis. This finding is most damaging when the company has been claiming scalability as a competitive advantage.
Security incidents that weren’t disclosed. Previous data breaches, credential compromises, or security vulnerabilities that were patched without disclosure create both legal liability and trust concerns with investors.
Single points of failure in key personnel. If the entire codebase is understood by one engineer who is not a founder and has no vesting cliff remaining, that’s a flight risk that technical reviewers will flag explicitly.
Vendor lock-in that wasn’t disclosed. Dependency on a single third-party provider — a proprietary model API, a specific data vendor, a sole-source infrastructure partner — without disclosed mitigation planning creates concentration risk that affects the investment thesis.
How to Prepare Your Technical Stack Before Fundraising
The right time to prepare for technical diligence is 3–6 months before you expect to start fundraising — not the week you receive the request. Specific preparation steps:
Run your own technical audit. Engage a senior technical advisor or fractional CTO who isn’t in your day-to-day operations to review your architecture, codebase, and infrastructure with fresh eyes. Identify the three or four findings that would most concern a VC technical reviewer, and create a remediation plan with timelines.
Document your architecture. Write a clear architecture document — 3–5 pages — that describes your system components, how they interact, where your data lives, and what your scaling strategy is. This document becomes the anchor for technical diligence conversations and forces clarity in your own team about architectural decisions.
Reach 70%+ test coverage on critical paths. You don’t need 100% test coverage across the entire codebase, but your core product functionality — the features customers pay for — should have automated test coverage that gives reviewers confidence in stability.
Clean up secrets and access controls. Audit your codebase for hardcoded credentials, API keys, or passwords. Implement a secrets management system (HashiCorp Vault, AWS Secrets Manager) and rotate any credentials that may have been exposed. This is both a security and due diligence preparation step.
Prepare incident history documentation. Document your three most significant technical incidents in the past 12 months — what happened, how long the resolution took, and what you changed as a result. Proactive disclosure of handled incidents demonstrates operational maturity; discovered incidents you hadn’t mentioned suggest opacity.
Managing the Technical Diligence Process
Once technical diligence begins, your goal is transparency combined with controlled information flow:
Designate a single technical diligence contact. Your CTO or most senior engineer manages all technical diligence interactions. Having multiple engineers answer questions independently creates inconsistency and reveals organizational confusion.
Set the agenda for the first call. Don’t let the reviewers free-form explore — propose an agenda that covers the areas you’re strongest on first, builds confidence, and addresses expected concerns in a prepared way. “Here’s what we’d like to walk you through” is a professional and effective opening.
Answer questions directly. Technical reviewers respect engineers who say “we have technical debt here and here’s our plan to address it” more than engineers who deflect, minimize, or over-explain. Honesty about known weaknesses with credible remediation plans is more reassuring than claimed perfection.
Provide a code review environment, not production access. Create a clean repository with representative code for review — you don’t need to provide production credentials or access to live customer data. A prepared code sample environment is standard practice.
Follow up with written answers. After technical calls, send a written summary of questions asked and your answers. This creates clarity, prevents miscommunication, and demonstrates organizational thoroughness.
Suggested Visuals
- Graphic 1: Technical due diligence process timeline — from term sheet to close, showing when each review category typically occurs
- Graphic 2: Nine evaluation areas radar chart — showing relative weight of each area by fund type (AI specialist vs. generalist vs. enterprise software)
- Graphic 3: Red flags severity matrix — impact on deal outcome vs. prevalence across early-stage startups
Frequently Asked Questions About Technical Due Diligence
Does every VC round require technical due diligence?
Not every round — seed rounds with pre-product or early-product companies typically skip formal technical diligence. Series A and beyond for technology-centric companies almost always include some level of technical review. The depth varies: a Series A may involve a two-hour call with a technical advisor, while a Series C at a deep tech company may involve weeks of codebase review by an external firm.
Can technical due diligence kill a deal after a term sheet is signed?
Rarely, but yes — particularly if technical findings reveal information that was inconsistent with representations made during the fundraising process. Undisclosed IP ownership gaps, undisclosed security breaches, or architecture that is fundamentally misrepresented in the pitch are findings that can result in deal termination. More commonly, technical findings result in reduced valuation, added conditions, or extended closing timelines.
What’s the difference between technical and product due diligence?
Technical due diligence focuses on the implementation — architecture, code quality, infrastructure, security. Product due diligence focuses on the product strategy, user experience, feature roadmap, and product-market fit evidence. They often happen in parallel, conducted by different reviewers. Technical reviewers ask “how was this built?” while product reviewers ask “why was this built, and is it working?”
How long does technical due diligence typically take?
For Series A raises, technical diligence typically takes 1–3 weeks from initiation to completion. This includes an initial architecture call (1–2 hours), a codebase review period (1–2 weeks), follow-up questions, and a final summary call. Growth-stage raises with larger codebases and third-party reviewers can take 4–6 weeks.
Should I engage a technical advisor to help prepare for diligence?
Yes — particularly if your founding team doesn’t include a strong technical leader who has been through the diligence process before. A fractional CTO or senior technical advisor who has experience with VC technical reviews can identify the findings that are most likely to surface, help you prepare documentation, and coach your team on how to present technical decisions credibly. The cost of that preparation is typically far less than the cost of a delayed or repriced round.
