Assumption Killer — Systematically Evaluate Your Assumptions

Assumption Killer is a free browser tool for anyone who needs to turn vague hunches into evidence-backed conclusions. Enter an assumption, add the evidence you have (for and against), assign confidence scores, and the tool surfaces whether your belief holds up — all running locally in your browser.

The Problem With Untested Assumptions

Every product, project, and decision is built on a stack of assumptions. "Users want this feature." "The market exists." "This architecture will scale." Most of these go untested because the process of evaluating them formally feels expensive.

The result: teams invest weeks in directions that collapse the moment they talk to a real user. Founders build products for problems that don't exist at the scale they imagined. Engineers optimize systems based on beliefs about bottlenecks that were never verified.

Assumption Killer makes the evaluation process fast enough to actually happen.

How It Works

Name the Assumption

State your belief clearly and specifically. "Users will pay for this" is too vague. "B2B users in the SME segment will pay $99/month for automated invoice reconciliation" is testable.

Add Evidence

For each assumption, add evidence items — observations, data points, user quotes, experiments, or research findings. Tag each item as supporting or contradicting.

Score Confidence

Assign confidence scores to each piece of evidence. Weak anecdotal evidence scores low. A controlled experiment with 50 users scores high. The tool weights your conclusion accordingly.

Get a Verdict

Assumption Killer computes an overall confidence level for the assumption based on the balance and strength of your evidence. You see at a glance whether the assumption is validated, invalidated, or still uncertain.

Why Local Processing Matters

Your assumptions are often the most sensitive strategic information in an early project. They're what you know that competitors don't. Assumption Killer processes everything client-side in your browser — no server receives your inputs, no analytics logs your decisions. It's a thinking tool, not a SaaS product that owns your insights.

Who Uses It

• Product managers evaluating whether a feature assumption survived discovery
• Founders working through a lean validation loop before building
• Researchers and analysts structuring evidence for or against a hypothesis
• Engineers deciding whether a proposed optimization is based on measured data or intuition
• Anyone who has shipped something and later thought "we should have challenged that assumption earlier"

Technical Details

Assumption Killer runs entirely in the browser. All processing is JavaScript. There are no API calls, no accounts, no persistent storage beyond what your browser provides. The tool is intentionally simple — structured enough to enforce rigor, fast enough that you'll actually use it.

If you've ever looked back at a failed project and traced the failure to an assumption nobody questioned, Assumption Killer is built for the next one.