Technical Due Diligence for Investors: What to Look For Before Writing a Check

If you're an investor about to write a check for a technology startup, the code behind the pitch deck matters more than the pitch deck itself. 73% of startup failures cite technical problems — not market fit, not funding, but the inability to build and scale the product. Technical due diligence tells you whether the code can support the growth story the founders are selling.

What technical due diligence actually evaluates. It's not a code review — it's a risk assessment. You're evaluating: (1) Can this architecture scale to 10x the current load? (2) Is the codebase maintainable, or is it held together with duct tape? (3) Are there security vulnerabilities that could become liability events? (4) Can the team hire and onboard new developers efficiently? (5) Is there vendor lock-in that creates business risk? (6) Does the technology support the product roadmap, or will a rewrite be needed?

Architecture assessment. Ask the CTO to walk you through the system architecture on a whiteboard (or Excalidraw). What you're looking for: Clear separation of concerns — frontend, backend, database, third-party integrations should be distinct layers. Scalability path — can they add capacity by scaling horizontally (more servers) or do they need to redesign? Single points of failure — what happens if the database goes down? If the primary developer leaves? Data model — is the database schema well-structured, or are there 'god tables' with 50+ columns? The architecture doesn't need to be perfect — it needs to be evolvable.

Code quality signals. You don't need to read every line of code. Look for: TypeScript or equivalent type safety — untyped codebases in 2025 are a maintenance nightmare. Test coverage above 50% (80%+ for critical paths) — tests prove the code works and make refactoring safe. Consistent code style — linting, formatting, and conventions applied uniformly. Git history — are commits descriptive? Is there code review (PRs with comments)? Are deployments automated? A clean Git history indicates professional engineering practices. Documentation — at minimum, a README that explains how to run the project, API documentation, and architecture decision records.

Security checklist. Non-negotiable items: (1) Authentication — are they using a proven auth provider (Auth0, Supabase Auth, Clerk) or a custom implementation? Custom auth is a red flag. (2) Data encryption — is sensitive data encrypted at rest and in transit? (3) API security — are endpoints authenticated? Is rate limiting implemented? (4) Dependency management — are dependencies up to date? Are there known vulnerabilities? (Run `npm audit` or equivalent.) (5) Secrets management — are API keys in environment variables, or hardcoded in the codebase? One hardcoded secret is a critical finding.

Team capability assessment. The technology is only as strong as the team building it. Evaluate: Bus factor — how many people need to be hit by a bus before the project can't continue? If it's 1, that's a risk. Hiring pipeline — can they realistically hire the developers they need? If the stack is exotic, hiring is harder. Technical leadership — does the CTO make architecture decisions based on engineering judgment, or on resume-driven development? Development velocity — how many features ship per sprint? Is the pace sustainable or are they accumulating technical debt to hit milestones?

Red flags that should make you pause. (1) The CTO can't explain the architecture clearly — complexity without clarity means they've lost control. (2) No test suite — the code works by accident, not by design. (3) Monolithic deployment with no CI/CD — manual deployments are error-prone and slow. (4) The entire codebase was written by one person who left — you're investing in an orphaned codebase. (5) 'We'll rewrite it after funding' — this almost never happens. You're funding the current code, not the hypothetical rewrite.

The output of a tech due diligence. Deliver a structured report with: Green flags (strengths to highlight), Yellow flags (risks that are manageable with a plan), and Red flags (risks that could threaten the investment). Include specific, actionable recommendations for each flag. A typical due diligence takes 2–3 days of a senior engineer's time and costs $3,000–8,000. Compared to a $500K+ investment, it's the cheapest insurance you'll ever buy.