The side project that becomes a company is the founding myth of the modern startup era — built nights and weekends, validated by strangers, quit-toward when the numbers said go. It is also a legal minefield whose blast radius includes the venture you left, the equity you earned there, and sometimes the ownership of the thing you built. Employment attorneys and venture counsel spent the 2020s cataloguing the disputes; the pattern is stable, and it starts with two documents almost every employee signs and almost nobody reads.
Amjilt News publishes information, not legal advice — this is a read-your-own-documents situation, ideally with counsel.
What's in those documents?
Three clauses, in varying combinations and enforceability. Invention-assignment agreements: broadly worded provisions assigning employee inventions to the employer — sometimes all inventions, sometimes those related to the employer's business or developed with its resources, with state-law limits (California's Labor Code section 2870 and its imitators carve out purely personal, off-hours, un-resource-using work). Moonlighting and conflict policies: prohibitions or disclosure requirements on outside work, especially competitive work. And non-competes — unenforceable for most workers federally since the FTC's rule attempts and state-law variation produced a checkerboard, with the 2024 federal rule's fate contested into 2025 but state hostility to non-competes broad in tech centers. The stack determines whether your nights-and-weekends project is yours, theirs, or grounds for termination.
What do the disputes actually turn on?
Resources and relatedness. The consistent fact patterns in the case law and counsel's advisory files: employees who built on company laptops, in company cloud accounts, during hours they were paid for, or in domains adjacent to their employer's — and then discovered the assignment clause reached the result. Courts and arbitrators look at the mundane evidence: device logs, timestamps, repository commits. The founders who kept their projects cleanly did the boring things from day one: personal hardware, personal accounts, strictly off-hours, documented. The ones who lost mixed a Tuesday-afternoon commit into the history and lost the argument along with it.
What about the duty of loyalty?
The doctrine that outlives the non-compete wars. Even where contracts permit outside projects, employees owe an employer fidelity while employed — no soliciting customers or coworkers for the venture, no using confidential information, no competing while on the payroll. The recurring mistake documented in departure litigation: founders who did their market validation — customer conversations, recruitment approaches — while still employed, converting a lawful side project into a breach. The clean sequence, per counsel's standard advice: build the product, quit the job, then sell. It costs months and saves the company.
How do employers handle this now?
Predictably varied. Some run disclosure regimes — side-project registration with approval workflows, which surveys suggested employees underuse by wide margins, for reasons the underuse itself demonstrates. Others tightened assignment language after watching alumni companies bloom, producing the current tension: employers want talent that builds, talent builds on the side, and the same aggressive clauses that protect IP also signal "leave here before you start anything." The AI boom sharpened it — moonlighting into AI startups became common enough that major employers issued explicit policies restricting outside AI work in 2023-2025, several of which made news precisely for the questions they raised about employer reach into employees' own time.
What's the pre-flight checklist?
Five items, before the project gets serious. Pull your invention-assignment, moonlighting, and confidentiality agreements and read them actually. Map your state's protections — the 2870-style carve-outs matter enormously by geography. Quarantine resources ruthlessly from the first line of code. Keep a dated record of work hours and tools. And when the signal says go — the traction, the pull — have counsel review the separation before, not after: the exit conversation, the final paperwork, the acknowledgment of obligations. The companies built this way start clean. The ones that start messy spend their seed round on the lawsuit instead.
FAQ
Can I build a startup while employed?
Often yes, depending on your agreements, state law, and whether the work uses employer resources or overlaps its business. Clean separation — personal hardware, off-hours, unrelated domain — is what keeps it yours.
Who owns my side project if I used company equipment?
Potentially your employer — assignment clauses plus evidence of company resources (devices, accounts, paid time) have repeatedly transferred side-project IP. State carve-outs like California's 2870 protect only strictly personal, off-hours, resource-free work.
For more context, read Founder vesting is where good breakups are decided years early.
For more context, read founder burnout.
For more context, read The acquihire math nobody explains until it's your company.