Specification

Whatever you fail to put in this document on the day you file, you can almost never add later. That single fact explains most drafting advice you will ever hear.

In simple words

The written document filed with a patent application: it describes the invention, how to perform it, the best method known to the applicant, and (in a complete specification) ends with the claims.

Think of it as

A frozen photograph of everything you knew on filing day.

Why it matters

The specification is the only permitted support for your claims. If a limitation is not disclosed in it, you cannot rely on that limitation to distinguish prior art later, no matter how true it is.

A simple example

You file describing a coating applied “by spraying”. Two years later the examiner cites prior art that sprays, and you want to amend to “applied by dipping”. If dipping was never described, that amendment is not available to you.

Common mistake

Writing only about the version you built. Alternatives, ranges, materials and failure modes you thought about but did not build belong in the specification too.

Where it comes from

Patents Act 1970 - section 10, contents of specifications