Multiple search terms within a single input box are combined with a boolean OR, so a search for the keyword lorde tresurar will locate letters containing the words 'lorde' or 'tresurar' or both words.

An exact phrase can be searched for by enclosing the search phrase in double quotes. A search for the keyword "lorde tresurar" will locate letters containing the exact phrase 'lorde tresurar'

Minus and plus can be used to specify whether a word (or exact phrase) must or must not occur in a lettter. A search for the keyword +lorde -tresurar will return letters that contain the word 'lorde' but not the word 'tresurar'. The boolean operators && (AND) and || (OR) can also be used.

The symbols * (zero or more characters) and ? (exactly one character) can be used as wildcards. A search for lord* will find 'lord', 'lorde' and 'lordship'. Wildcards cannot be used at the start of words or in exact (double-quoted) phrases. A search for frend? will find ‘frende’ and ‘frends’ but not ‘frendely’ ‘frendshep’ or ‘frinde’.

Keyword options can be combined to create complex queries. For example +"lorde tresurar" && -long?r && +long* searches for letters that must contain the exact phrase "lorde tresurar" and must contain at least one word beginning 'long', but must not contain any words of the form 'long?r' (e.g. longer, longor, longar).

The keyword search only searches the text of the letters, and not the metadata associated with the letters. The boolean relationship between input boxes is AND, so a search for the keyword: lorde tresurar and sender: wylliam cauendish will only find letters sent by William Cavendish which contain 'lorde' or 'tresurar'.