A hard search is a credit check that is recorded on a file and can be seen by other lenders. It is usually run when a full application is made, and several in a short time can lower a credit score temporarily.
In one line: A hard search is a recorded credit check, visible to lenders, that can dent a score if several happen close together.
How a hard search works
When a formal application for credit is submitted, the lender runs a hard search that is logged on the credit file. Other lenders looking at the file later can see that search and the date it was made.
A single hard search has a small, short-lived effect. Five card applications in a month leave five hard searches, which can look like urgent demand for credit and weigh more heavily on scoring.
Hard searches typically stay visible on a file for around twelve months, although the scoring impact usually fades well before they drop off.
Hard search vs soft search
A hard search is visible to other lenders and can affect a score. A soft search is visible only to the file holder and does not.
Eligibility checkers use soft searches to estimate acceptance, so checking likely eligibility first can avoid unnecessary hard searches from applications that would be declined.
Primary source: Information Commissioner's Office: credit reference files
