A patent keyword search is a type of patent search that helps you locate patents similar to your invention by looking up keywords in various patent databases. By doing a patent keyword search, you get a good sense of whether your invention can be patented or a competing patent already exists. You can only get a patent for an invention no one has thought of before. 

It is important to remember that just because you have never seen something like your invention does not mean you are the first person to think of it.

Why Is a Patent Keyword Search Important?

A patent keyword search is an important step in preparing your patent application. This kind of research helps you do several things:

  • Find previous patents or information that might show someone else already thought of your invention.
  • Find out who owns a patent related to your invention.
  • Find other inventors who can help you prove or disprove the validity of your patent application.
  • Find related technology that may help with your patent application.
  • Find new opportunities for future inventions.
  • Show that you have done your homework. This is helpful if you want to sue someone for patent infringement or if someone sues you.
  • Identify potential competitors.

Information In a Patent

  • General information
    • Title
    • Summary of invention
    • Name(s) of inventor(s)
    • Name of the patent owner
    • Dates and filing numbers
    • Status of the patent
    • States where patent would apply
  • Technical information
    • Technical description
    • Drawing of invention
  • Additional drawings & description of what is protected
  • Search report

Kinds of Patent Keyword Searches

Some tools search patents' full text. These are usually called full-text databases.

Others search patent summaries. Summaries are usually made up of the information on the first page. These tools are often called bibliographic databases.

In addition to the information on the first page, bibliographic databases often include:

  • An abstract, or short description of the patent
  • Classification codes
  • Related patent numbers and dates
  • Images or drawings
  • Keywords

Bibliographic databases put the same kind of information in the same place for each patent in the database. These are called informational fields. They make it easier to find what you are looking for.

Patent Classification Search

A patent keyword search is just one of several approaches to patent searching. There is also a method called patent classification search. This involves finding and searching the patent classifications that are likely to be relevant to your invention.

A classification system is a hierarchy that organizes technologies according to what they do, how they do it, what they are made of, and how they are made.

However, a patent classification search has challenges and limitations. There are many patent catalogs around the world. These are broken into:

  • Classes, which you can think of as big buckets
  • Subclasses, which are like smaller buckets within the big one

(The International Patent Classification also uses Sections and Groups. Sections are larger than Classes, and Groups are smaller than Subclasses.)

Right now there are more than 450 classes that separate one technology from another. There are more than 150,000 subclasses that organize each class.

Patent classifications are changed, merged, and deleted over time. This is especially true of emerging technologies. So while all related patents should be grouped together, this is not always the case. Examiners will search every classification to decide if your invention is eligible.

A given class or subclass may contain tens of thousands of patent records, so it is best to use a patent classification search to locate the right classifications. Then use keyword searches to filter the results.

Prior Art

Prior art is another term for "state of the art." It refers to all previous information about a specific science or technology. Any public document published before the patent application date can be considered prior art. When you do a patent keyword search, you are trying to find any prior art that is similar to any part of your invention.

You should search for prior art throughout the 18-month patent publication process. The search will give you new keywords to add to your research. Keep in mind, if you don't find any prior art, that doesn't necessarily mean your invention is new.

You might find prior art that shows someone else already thought of your invention. But you might also find prior art that shows how your invention is different than other inventions in the same field. This can help confirm your patent application during the investigation process.

Boolean Operators, Proximity Operators, and Search Codes

These are words and codes you use to narrow the results of your search. They include:

  • And: Used to search for two words at once, like "tire AND tyre"
  • Or: Used to search for one keyword or another, like "tire OR tyre"
  • NOT: Used to exclude some results, like "tire NOT bicycle"
  • NEAR/#: Used to specify the number of words between two keywords
  • ABST: Used to search abstracts
  • SPEC: USed to search specifications or descriptions
  • CCL: USed to search current classifications
  • AN: User to search owner or assignee names
  • IN: Used to search inventors names

Which Boolean operators and search codes you can use, if any, depends on the tool you are using.

You can also use parentheses to combine Boolean operators within a search string, like "skateboard OR (skate AND board)."

Garbage In Garbage Out (GIGO)

This means a search tool is only as good as the information in it. If someone puts inaccurate, incomplete, or incomplete information in the system, the results will have the same problems.

Read Patents

One of the best ways to prepare for your patent keyword search is to read a lot of patents. By reading patents related to your invention, you will find new keywords. You will also get more familiar with the format and content of a patent.

You can also find useful information by reading patents. For example, look at the "U.S. Cl." and "Field of Search" sections for other classes and subclasses that might be helpful in your search.

Give Yourself Enough Time

Many new inventors underestimate the amount of time a search takes. You should plan to spend one-third of your project time on patent keyword searching.

Outsourcing Your Patent Keyword Search

It is possible to hire a professional to do your patent search. Some companies offer tools to help you come up with keywords or semantic search strings. However, they usually charge between $1,000 and $2,400.

There are, however, benefits to hiring a professional to help. Patent classification systems are complicated and confusing. Patent search professionals know the systems well. This means they can find the right class, subclass, and even secondary subclass quickly and accurately.

Patent Keyword Search Strategies

Find Your Keywords

A patent keyword search only gives you results that match your keywords exactly. For that reason, it is critical to have the right keywords.

First, think about all the different aspects of your invention:

  • What is it made of?
  • How does it work?
  • What is its basic function or purpose?
  • What is the result?
  • What industry or market does it belong to?

Next, try to come up with keywords related to each of these aspects that might help you find relevant prior art. These should include specific, general, technical, descriptive, and related keywords. Then group them together in every possible way and do searches.

The USPTO offers a seven-step guide to patent searches. This includes questions to help you brainstorm good keywords.

As you do this, you will find other keywords related to the ones you are using. For example, once you find the class and subclass for your invention, you may see other items or subclasses containing useful keywords. Add these to your list of keywords to expand your search.

Inventors often apply for more than one patent in the same area. So if you notice an existing patent or application that is relevant to your invention, note the person's name. Add it to your keywords.

You will also notice the names of Patent Examiners. These are the people who investigate patent applications. They often specialize in certain areas. Add their names to your keywords too.

When you find patents related to your invention, make a note of the patent number. You can use this information to help with more searches.

Think about people you know who are subject matter experts (SMEs) in the area you're researching. Ask them for help in developing keywords.

Alternate Approach To Finding Keywords

  • Search for the general concept of your invention.
  • Narrow the results down to the right class.
  • Use the NOT operator to exclude the original concept.
  • Find synonyms for the original concept and exclude them with the NOT operator.
  • Keep a list of your NOTs.
  • Keep doing this until you have found almost all the patents in the class.
  • Now use those synonyms to do a new search with no NOT or class restrictions.

Find the Right Class and Subclass

In each classification system, use keywords, operators, and search codes to find the right class and subclass for your invention. Then verify that you have the right class and subclass.

You can look at the list of subclasses to get a good idea of how the class is organized. This will make it easier to find the right subclass for your invention.


Be sure to document every search you do. Use a notebook or computer to record your search terms and results.

You should also keep a patent document library. This is a collection of all the useful documents you find in your research. You can use these documents in your patent application to help prove eligibility.

Navigational Search

You do this kind of search when you know a patent exists and you are trying to find it.

Research Search

You do this kind of search when you are learning about prior art in the area related to your invention.

Semantic Search

You should be aware of semantic search. This is an alternative to keyword search.

Keyword search involves sifting through huge amounts of information to find what you're looking for. Semantic search aims to narrow down the information you search through to make it easier to find relevant results. Instead of focusing on exact keywords, semantic search uses the concepts behind the keywords to find search result more quickly.

Semantic search uses algorithms to look for patterns in language and phrasing. Patent authors tend to use words and phrases consistently. This type of search takes advantage of that. It is especially good for finding results that use vague language or new or uncommon terms.

A traditional keyword search can take 10 or more hours and result in a search string that is one or more pages long. Semantic search strings are just four or five words plus operators. Fans of semantic search say it gives you more results in far less time. That's time you can spend analyzing metadata, classification codes, and other search results.

General Patent Search Mistakes and Challenges:

  • Depending on the specifics of your search, you may get tens or even hundreds of thousands of mostly irrelevant results. These are known as false positives. Your search may fail to find results it should find. These are called false negatives.
  • Different patent examiners would classify the same invention differently. So even patent classification codes are not totally reliable.
  • It is not enough to search a patent abstract or summary. You should use a text-only service to search the full text of each patent. Otherwise, you may miss something important.
  • Many patent catalogs only go back a few decades. To search the full history of patents, use one that has a full back catalog.
  • Some people liked searching paper patent records. However, many databases are now only available online.
  • It is also not enough to only search patent records. You need to search the whole IP Lifecycle (patents, trademarks, and copyrights.)
  • Things like press releases, product announcements, technical guides, and news reports may also contain information relevant to your search. Also search any cited resources that you find. If any public document has evidence that someone thought of your invention before you did, you probably cannot get a patent.
  • Some patent search tools are expensive, so your ability to do a thorough search may depend on your budget.
  • No patent search is perfect. There are too many variables. All you can do is be as thorough as you can.
  • Remember to keep searching as your invention develops and changes.

Patent Keyword Search Mistakes and Challenges:

  • Patents are issued all over the world. So when you search international patents, you are searching translated documents. These translations may not be correct or may contain alternate keyword spelling.
  • The person who wrote the patent may use different words to describe his or her invention than you do. He or she may even have done it intentionally to complicate your search.
  • There may not be a patent for the specific term you're searching for, but there may be a more general patent that includes that term. So be sure to search for general keywords as well as specific ones.
  • Patent applicants often invent new terminology that you don't know to search for.
  • Some words have more than one meaning or look/sound like other words. These can lead to confusing search results.

Patent Classification Search Mistakes and Challenges:

  • There are several classification systems, including:
  • Each classification system is interpreted differently depending on who uses it.
  • Classification systems vary in how broadly or narrowly they are defined. The CPC and Japanese systems are highly defined. The IPS is commonly used but very broad. The ECLA is a more narrow extension of the IPC. The USPC is in the middle.
  • Classification systems also vary in how often they are updated. The IPC is updated every five years, but that may be too slow for technologies that change quickly. Some patent offices, like the United States Patent and Trademark Office (USPTO) try to stay more current.
  • Your invention may use things that fall under different classes or subclasses. If so, you may need to decide which is a better fit. You may also decide to search in more than one class and subclass, or that the right class and subclass is not available.
  • Use a technical thesaurus like INSPEC or MESH to find keywords like the ones you are using.
  • Search classification systems with free tools like the USTPO Manual of Patent Classification and Espacenet's ECLA search.
  • Search the World Intellectual Property Organization (WIPO) by IPC number or keyword.
  • Use the popular free patent search site Free Patents Online. It is faster than the USTPO site and offers patent images.
  • Use the USTPO's Advanced Search Tool.
  • Use Google Patent Search. However, be aware that it searches limited fields and there are some holes in the information it contains.
  • Use Espacenet to search patents and patent applications from Europe and other international countries.
    • To do a Quick Search, enter:
      • The collection you want to search
      • Whether you want search words or names
      • The keywords you want to search for
    • The advanced search allows you to combine search items and use operators. You can search the following fields:
      • Title
      • Title or abstract
      • Publication number
      • Application number
      • Priority number
      • Publication date
      • Applicant
      • Inventor
      • European Classification (ECLA)
      • International Patent Classification (IPC)
  • Search for issued patents and patent applications through the USTPO's PATFT and AppFT tools.
  • Refer to the USTPO's Seven-Step Patent Search Strategy Guide.
  • Read the USTPO's Overview of the U.S. Patent Classification System.

If you need help with a patent keyword search, you can post your question or concern on UpCounsel's marketplace. UpCounsel accepts only the top 5 percent of lawyers to its site. Lawyers on UpCounsel come from law schools such as Harvard Law and Yale Law and average 14 years of legal experience, including work with or on behalf of companies like Google, Menlo Ventures, and Airbnb.