How ProofPrice earns trust
A price is only useful if you can check where it came from. These are the rules we keep, and how we check that we keep them.
Official and licensed sources only
Every figure comes from official open data, licensed data, partner data or (later) verified receipts. Today that is 21 official sources, each listed with its publisher, licence and limits on /sources. We do not scrape sites in breach of their terms. Where a publisher's licence wording is still being confirmed, the licence line on /sources says so.
What every answer carries
- Source and licence: the publisher, a link to the licence and the attribution line to show when you reuse the figure.
- Sample size: how many records the figure is built from.
- Period: the dates the records cover.
- Confidence: high is 50 or more records, medium is 15 to 49, low is 5 to 14.
- Method: a plain description of how the median and the typical range (10th to 90th percentile) were worked out. See /method.
- Price type: whether the figure is a recorded sale price or a posted price.
Aggregates only, and never a thin figure
We publish ranges, not individual records. For home sales we never return an address or any personal data. We never publish a figure from fewer than 5 records: below that, the answer says there is not enough data. See the privacy notice.
Asking prices are never shown as paid prices
Home figures are recorded sale prices. Fuel figures are posted pump prices, and they are labelled that way, because they are what each station displays, not a receipt. A listing or asking price is never presented as something people paid.
How a source is checked before it goes live
- Found. We identify the official publisher and the dataset.
- Licence checked. We record the licence, its link and the attribution line, and what the data may and may not be used for.
- Real format proven from a server. We fetch the real file or feed from a server and build the reader against what it actually returns, not against its documentation.
- Tests. Automated tests run against a sample copied from the real format.
- Preview checks. The source is tried on a private preview deployment before it reaches the public site.
- Production smoke tests. After release, each source's example request is run against the live site and must return a valid answer.
After release, every live source is monitored twice a day. The state of the daily price library is on /status.
The daily price library
Once a day we take a snapshot of each source that supports history (9 today) and keep, for each place and item, only the median, the 10th to 90th percentile and the count. Days with fewer than 5 records are not kept. The latest figures are published as pages you can read at /prices.
Corrections
If you think a figure is wrong, report a wrong figure to hello@proofprice.com. Tell us the request you made and what you expected. If the mistake is ours, we correct it. If the official source is wrong, we cannot change the publisher's data. We do not promise a turnaround time.
Limits
ProofPrice gives information, not a valuation, quote or offer. Ranges describe past recorded prices. Read the terms of use before you rely on a figure for a big decision.