How to write a patent description

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This is part of a series of articles on the basics of writing a patent specification. The full series covers the description, claims, drawings and abstract. The overview article and starting point is “How to write a patent specification“.

The series uses a silly, fictional invention as an example: a rotary cutter for shearing sheep. This is probably a terrible invention but, in reality, most are.

The description is the meat and bones of a patent specification. It describes what the invention is and what it does, it explains what its advantages are, and it describes variations and modifications that could be made to the core idea. Importantly, it must provide sufficient information to enable a skilled reader to make the invention. You cannot patent an invention and also keep its essential details a trade secret.

A common error when writing the description is to put everything in vague or overly general terms. The motivation behind this error is the fear that precision means that a competitor could easily work around a granted patent with a minor modification. But vague writing hobbles the whole specification and reduces the chances of obtaining any granted patent at all. The key is to write with clarity and precision and then to build carefully crafted generalities onto that solid foundation.

A description is made up of three main sections, the Background, the Summary and the Detailed Description.


The Background section describes the field of the invention and its context within known technology.

Start with a title in capital letters. The title should be short and identify the general field of the invention without giving away all the details. We don’t need to immediately know what the invention’s novel features are. “Sheep shearing device having a motorised, rotating, cutting blade” is too much information. “Sheep shearing” is enough to tell the examiner what is coming next. “Cutting” goes too far in the opposite direction since this could be anything from toenail clippers to an industrial, sheet metal laser cutters.

A lot of specifications have titles starting something like “Device and method for…”. Sometimes this is done in an effort to make the specification sound more formal and more like a “proper” legal document. Get out of this habit right at the start. These phrases are superfluous and might end up being wrong if the method claims are all dropped during examination of the patent application.

Immediately after the title, write a short paragraph of no more than a sentence or two to confirm the field of the invention. “The present invention relates to shearing of sheep and other fleeced animals” could be enough.

One aim with the field of the invention is to get the patent application to the right examiner. Patent examiners specialise in different ares of technology and the field of the invention helps with the initial categorisation by the Patent Office. Helping the Patent Office to do their job can only benefit a patent application.

The Background section then summarises the prior art. This is a story for the patent examiner to get them interested and in the right frame of mind. It is where the writer’s inner novelist must shine through. Describe things that are already known, referencing earlier patents covering similar ideas where possible. Then point out the terrible shortcomings and problems with these earlier ideas. What the world really needs is a new invention that solves these problems! Hurrumble!

There are two main aims here. First, set up some problems the invention solves, without making the solutions look obvious when they come. There needs to be something of an “a-ha!” moment when the examiner reads the Summary section of the description.

Second, get the examiner interested in knowing what the invention is. Examiners read hundreds of specifications and are typically experts on the subject matter. Don’t lecture them or patronise them or they’ll switch off before they’ve reached the invention. Keep the Background brief and focused on setting up the big reveal that is the invention.

As well as setting up the invention for the examiner, the Background is a great way to focus the writer’s mind on what the invention really is. Take the time to research and understand the current state of the art and why there is a need for something better. This doesn’t require a full patent prior art search. Simply reading up on Wikipedia or on a few trade websites can help get the lay of the land.

Having done the research, try to find one or two problems the invention solves. Be honest with yourself about it. If everything about the invention looks obvious or pointless, perhaps it should be sent back to the drawing board and developed a little further. On the other hand, an invention doesn’t need to be groundbreaking. Just one incrementally novel feature can make a great patent.

This is the first section of the specification that should be written in order to form some early ideas of where the focus of the invention lies. Be prepared for these ideas to change as the details are written out in full but make sure you’re largely happy with this section before going on to the rest of the specification.


The Summary section describes the essential features of the invention and the advantages that those features provide. The solutions to the problems with the prior art set up in the Background are finally revealed.

In its final form, the Summary is simply a copy-pasted list of the claims. Then, after each claim, the advantages provided by the claimed feature(s) are fleshed out one at a time. For this reason, it is usually the last part of a patent specification to be written. It is an opportunity to take the bare and legalistic style of the claims and add a more emotive sales pitch for the benefit of the examiner. Show the examiner why the invention is great, and they will be more invested in it and more willing to grant it a patent.

It is important to be honest about exactly what advantages are provided by individual claimed features. The finished product may have many bells and whistles which do marvellous things as a whole. The claims, however, present the invention in a piecemeal fashion and it is necessary to break down exactly why each feature on its own adds something advantageous. If it doesn’t, perhaps it shouldn’t have a claim to itself.

In the first draft of the specification, jot down the initial ideas from writing the Background section about what problems are solved by the invention. Update this list with new ideas while writing the Detailed Description section, then refer back to them when writing the Claims section. Once all these ideas are covered in the claims, scrap the list and write the Summary out in full based on the final claims.

Detailed Description

The Detailed Description is usually the longest section of a patent specification but the most straightforward.

Writing it is simplified if you have a good set of drawings which clearly show all the key features of the invention. Order the drawings in a way that will create a coherent structure for the description. The description starts with a one-line summary of each drawing to set the scene. Much of the work is then a mechnical process of going through each drawing in turn, describing it as clearly and precisely as possible, explaining how the invention works and how it is used. Add sequential reference numbers to individual features as you go, but using multiples of 5 or even 10 in case you make an error and need to come back and fill in a gap later.

Imagine if the drawings went missing. The Detailed Description is good if you can recreate the drawings from the text alone. Given the adage that a picture is worth a thousand words, that means a lot of text! Avoid too much jargon and define any jargon you do use. Use a dictionary for important words or definitions. You will be surprised at how often a word does not mean what you think it means.

Alongside the precise description of the drawings, the Detailed Description also discusses modifications that could be made. This is where the generalities are added to expand the basic invention.

One piece of the invention shown in the drawings could be in the shape of a cricle, but it could also be a triangle or many other different shapes. A bad description would try to generalise immediately and only say something like “a shaped piece”. This adds nothing of value to the specification. Instead, describe the piece as being circular and say what function it performs. Then explain that the piece could be different shapes and describe those shapes and how the different shapes and sizes affect the function of the piece.

The process is long and requires careful thought about different shapes, sizes, materials and combinations of different features that could be implemented by the inventor or a competitor. But it is important to go through it. If one variation has particular advantages over others, explain why, and then add that advantage to the list in the Summary section. A single advantageous variation could turn out to be the basis of a claim which gets the patent granted.

Example Description

Using all the lessons learned in this article, here is an example description for the sheep shearing device. It assumes the claims have been written and these have been copied into the Summary section. Also, do remember this is a wholly fictitious example, including a fictitious problem with the prior art.


The present invention relates to the shearing of sheep or other fleeced animals such as llamas.

Sheep shearing is an ancient profession and many different designs of shears are well known. Modern electric shears use a pair of linearly oscillating blades to remove the fleece.

Existing shears remove the fleece in large, tangled sections which must be separated during processing to create the finished wool. What is needed is a way of disentangling the wool as it is shorn.

The present invention provides a shearing device comprising a motorised rotary cutter.

Advantageously, the rotary cutter of the shearing device cuts small sections of fleece from the animal being shorn. These small sections are more easily disentangled during processing.

Preferably the shearing device comprises a raised lip around the perimeter of the rotary cutter.

Advantageously, the raised lip protects the skin of the animal from direct contact with the rotary cutter, preventing injury, but fleece passing over the lip is still shorn off by the rotary cutter.

Preferably, the raised lip is triangular in outline.

Advantageously, having a triangular raised lip ensures that a large section of the animal’s skin is protected from direct contact with the rotary cutter.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates a rotary cutting device; and

Figure 2 is a section through the rotary cutting device.

Figure 1 illustrates a rotary cutting device 5. The device comprises an electrical motor 10 and a rotary cutter 15 having six blades 20. Many different designs of rotary cutter are well known and could be used in place of the six bladed rotary cutter illustrated. In use, the electrical motor 10 causes the rotary cutter 15 to rotate. When the rotating blades 20 of the cutter 15 are brought into contact with the fleece of a sheep or similar animal, the fleece is shorn off in small, easily disentagleable portions.

A circular raised lip 25 surrounds the rotary cutter 15. As best illustrated in Figure 2, the raised lip 25 extends above the uppermost cutting surface of the blades 20. Consequently, even when the raised lip 25 is pressed against an animal in use, the blades 20 of the rotary cutter 15 are prevented from making direct contact with the skin of the animal, protecting it from injury. Nevertheless, the lip 25 has a perimeter of at least 2cm, preferably between 3cm and 6cm, to enable sections of fleece to easily pass the lip and be cut by the rotating blades 20.

The raised lip 25 is preferably circular in shape, as illustrated in the Figures, and matches the size and shape of the rotary cutter 15. Alternatively, the raised lip 25 is in the shape of a triangle. A lip 25 in the shape of a triangle flattens the skin of the animal over a relatively larger area, reducing the possibility of the animal being harmed. Many other shapes of raised lip 25 are possible, though preferably the lip is in the shape of a regular polygon.

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