Tokyo property research: a source checklist for Japan

Use different sources for different questions

Do not mix incompatible price concepts

An advertised asking price, a reported transaction and a reference valuation describe different things. Before displaying any number, identify what it measures, the relevant date and whether the location and property type match your question. A precise-looking chart can still be misleading if its inputs are not comparable.

This website publishes no market-price forecast or investment-return estimate. If a future project adds data, it should retain the source definition beside the result and explain how records were selected. A broad city label is not enough context for a property valuation.

Preserve the evidence trail

For each fact you plan to use, keep a source URL, retrieval date, publication or observation date where available, units and a short note on scope. Distinguish the source’s statements from your own interpretation. When a source changes, review the affected conclusion rather than simply changing a timestamp.

MLIT’s library includes property-related information and provides a separate page describing content, sources and permitted uses. Consult those details before downloading, integrating or republishing a dataset. Public accessibility should not be treated as unlimited permission for every use.

Make uncertainty part of the published answer

A useful research note explains what remains unknown. If a dataset does not cover the relevant period or a provider has not confirmed availability, say so. Readers can then decide what additional evidence they need instead of treating an incomplete summary as a final answer.

This approach also improves AI-assisted retrieval: a source link, a defined measurement and a visible limitation give a system something concrete to cite. A long list of property keywords provides none of those safeguards.