What is a constraint check?
A constraint check is a screening of one location against the official datasets that record planning-relevant designations and risks in England — run in seconds, from a pin on a map.
What "constraint" means here
A planning constraint is anything recorded in an official dataset that could affect what you can build, extend, or do with land: a conservation area boundary, a listed building, a tree preservation order, a flood zone, green belt, a site of special scientific interest, an area of outstanding natural beauty, contaminated land risk from historic mining, and around fifty other categories drawn from planning.data.gov.uk, Historic England, Natural England, the Environment Agency and the Mining Remediation Authority.
None of these datasets are proprietary or scraped — they're the same registers a planning officer or a professional search would consult, accessed through official APIs under the Open Government Licence (or, for HM Land Registry ownership data, HM Land Registry's own free licence). Every finding in the app names its source.
How a check runs
- You choose a point — an address, a postcode, a map click, or your current location.
- You choose (or accept the default) a search area — a small circle by default, or (with a paid plan) a wider radius, a drawn boundary, or the registered Land Registry parcel.
- The app queries each data source for anything that intersects your search area, or falls within it if the dataset is point-based.
- Each category comes back as Clear, a finding with distance and detail, or Partial if that particular source couldn't be reached — see Reading your results for why a failure is never allowed to look like a clean result.
What it's checking against, and what it can't tell you
Constraint checks answer "what does the official record say applies here?" They don't replace:
- A local plan policy review — a constraint check tells you a site sits in a conservation area; it doesn't interpret the conservation area's specific policy for your proposal.
- A planning application decision — only the local planning authority decides that.
- A legal search — for anything with money riding on it (a purchase, a loan, a planning submission), verify with the local authority or a professional.
Some designations aren't yet digitised nationally and won't appear even where they exist on the ground — this is a known limitation of the underlying open data, not something the app is hiding. Where we know a source is unreachable rather than simply empty, the result says so.
Role presets
Rather than showing every one of fifty-plus categories by default, you can pick a role preset (for example "homeowner extension", "developer", "consultant") that surfaces the categories most relevant to that kind of project first. You can always expand to see everything checked.
Where to next
- Reading your results — what each status means and how to interpret a finding.
- Saving sites — keeping a check for later, and turning on monitoring.
- Generating a report — turning a check into a PDF you can share or file.