Diagnostic System
Validate product decisions before scale makes them expensive.
ProductBooks is the diagnostic layer for Problem, Product, and Business Model decisions.
Start with Problem–Solution Fit. No sign-up required.
System Flow
Problem → Product → Model
Problem
Problem–Solution Fit
If the problem is weak, every signal above it misleads.
Product
Product–Market Fit
If users do not return, you do not have product–market fit.
Business Model
Business Model Fit
If margins break at scale, the model fails.
If one breaks, everything above misleads
- Product signals are invalid without a real problem.
- Business signals are invalid without real product pull.
Evaluate the system in order
Start at the lowest stage you can prove. Move up only when the stage below holds.
FAIL
Problem–Solution Fit
Truth test for problem pain and solution pull.
Output
Score 0 / 100[FAIL]
Signals
- Problem pain is still unproven.
- Solution pull has not been scored.
- Real user evidence is still missing.
What to do next
Run the stage to test whether the problem is real enough to continue.
FAIL
Product–Market Fit
Truth test for return behaviour, demand, and payment.
Output
Score 0 / 100[FAIL]
Signals
- Retention has not been validated.
- Demand may still be launch-driven.
- Payment behaviour is not confirmed.
What to do next
Run the stage once real users exist and repeat behaviour needs to be tested.
FAIL
Business Model Fit
Truth test for margins, founder load, and scale resilience.
Output
Score 0 / 100[FAIL]
Signals
- Unit economics are not verified.
- Founder dependency may still distort the model.
- Scale resilience is still unknown.
What to do next
Run the stage before treating growth, spend, or hiring as justified.
ProductBooks may tell you to stop
- Weak problem evidence should halt product confidence.
- Weak retention should halt growth confidence.
- Weak economics should halt scale confidence.
Evidence & Verdicts
Strict inputs only. Missing proof does not get the benefit of the doubt.
What counts as evidence
- Real users with verifiable source material.
- Observed behaviour before stated opinion.
- Payment or commitment before intent.
What scores zero
- Team belief, summary, or interpretation only.
- Enthusiasm without behaviour change.
- Forecasts used as proof of current demand.
Generate the evidence you do not have
Tools exist to improve the score. They do not replace the score.
User Survey Generator
GENERATEBuild behaviour-led surveys that expose real pain and current alternatives.
Used to improve
Problem existence and frequency evidence.
User Interview Generator
GENERATEBuild interview prompts that test pain, context, and failed workarounds.
Used to improve
Observed problem intensity and user context.
Prototype Test Generator
BUILDSet up low-friction prototype tests that force real reaction instead of polite interest.
Used to improve
Solution reaction and behavioural validation.
What to do next
Most teams should start with Problem–Solution Fit.
Validate the problem first. Product and model signals mean less if the foundation is still assumed.
Go to Problem–Solution FitRun the first stage before you commit more cost.
ProductBooks is built to show what still holds, what fails, and what evidence is still missing.