How to look for prior art using free tools; the importance of classification searching

There is no comparison between a patent search done by an inventor and a patent search done by a professional searcher.


Inventors and entrepreneurs who are looking to cut costs frequently conduct their own patent search. This is a wise first move, because patent searches are critically important.

But inventors must be careful. It is common for them to do a patent search and find nothing, even when there are things that could and would be found by a professional searcher.

So although it makes sense to do your own search first, be careful relying on your own search to justify spending the thousands of dollars you will need to spend to ultimately obtain a patent. Do not forgo a professional patent search. There is no comparison between a patent search done by an inventor and a patent search done by a professional searcher.

That said, every inventor should spend time searching and looking for two reasons:

  • Spending time patent searching familiarizes you with prior art.
  • Patent searches inform you on the prior art so you can focus on what makes your invention unique.

Of course, if you find something that is too close on your own, you save time and money and can move on.

Certain tools’ pros, cons

If you do your own searching and find relevant patents, you need to learn some strategies—and about the free tools that are available.

If you do your own preliminary patent searching, look at the United States Patent and Trademark Office patent search page. A lot of information can be found free, and the system is not terribly difficult to use.

There is also an excellent Help Section on the patent office website to educate inventors on how to use the online search features. Another excellent (and free) site that you should use when searching is Free Patents Online.

Whenever I search I tend to use Free Patents Online, simply because it is easier to access the patent illustrations. This leads me to one of the best things about Free Patents Online: It provides copies of the actual PDF documents, which is why it is easier to obtain access to the images. Using the images on the USPTO website to obtain these full text PDF documents that contain the images is cumbersome.

Free Patents Online is also normally much faster than the USPTO site as well, although I sometimes find the patent search engine of the patent office better. Nevertheless, when I use the USPTO patent search engine, I go to Free Patents Online for the PDFs and to access related patents, which is much easier because everything at Free Patents Online is hyperlinked.

So once you find a handful of relevant patents, go to FPO so you can easily jump back and forth and look at the patents that are cited in each relevant patent you find.

Google also offers Google Patent Search, which is lightning fast (unlike the USPTO online database) even compared with Free Patents Online.

The reason I don’t suggest this search tool first is because the Google Patent Search engine has serious limitations. The number of fields that can be searched pales in comparison to the USPTO or Free Patents Online.

Thus, if you are going to use Google Patent Search, it is probably best used initially because when you start a search you want to cast a very wide net—so the limitations of the field search are probably not as important initially. As you start to want to search for specific things, perhaps terms within a particular part of a patent or patent application, the Google tool is not very useful.

Google Patent Search also has some holes in the database. I have specifically looked for patents I know to exist and cannot always find them. I have heard the same experience from other patent attorneys and patent agents. Additionally, the most recent patents are not always available on Google.

What this means is you cannot only rely on Google, but you still must use it.

The Google database covers patents that are issued all the way back to U.S. Patent No. 1. This scope is much broader than either Free Patents or the USPTO. So although you might not find everything and it is difficult to specifically narrow your search, you still should use the Google database to see if there are old references that might be on point.

Advanced Search

When using the USPTO search features, either at the USPTO website or on Free Patents Online, one trick to improve search quality is to start by using the Advanced Search Page and searching in the specification field.

Let’s say you are looking for patents that relate to insulated containers for carrying beverages. You must pick a term or phrase that might appear within the written description of issued patents.

Following this example, you might try in the search box: SPEC/”insulating beverage container.” When this search was conducted, the results returned a list of 27 patents issued since 1976 that have used that phrase in the specification.

This points to the first problem encountered by doing your own patent search online at the USPTO. You can only do full text searching back to 1976. This is probably not too much of a concern for those operating in the high-tech sector but is important to know nonetheless.

The fact that you can only search going back to 1976 can be extremely detrimental if you have a mechanical invention or gadget.  It is not at all uncommon—in fact, it is extremely common—for inventors in every generation to seek solutions for the same or similar problems, which leads to the same or similar solutions/inventions.

In this case, there were not many patents from which to choose. Many times, however, the list will contain hundreds or even thousands of patents, depending upon the popularity of the term or phrase selected.

For example, if you search “SPEC/thermos,” you will find hundreds of patents that use this word in the specification—and that is only for patents issued since 1976. So what should you do now?

If you find too many patents, rework the specification field search. For example, if your search were “SPEC/thermos and SPEC/beverage,” you get down far fewer patents.

Ultimately, upon receiving manageable results, just click on several of the patents. The key is to start off broad and then narrow your way down to those that are the most likely relevant references.

Classification searching

Before going any further, it is worth pointing out one major problem associated with inventors doing their own search. What you are doing, at least in the first instance, is a keyword search.

Perhaps the reason there were only 27 issued U.S. patents found that use the term “insulating beverage container” in the specification is because that isn’t the proper, or at least most common, way patent attorneys and patent agents typically describe that particular feature set.

This means it is essential to try a variety of different keywords in your search. I’ve done searches using keywords in the past and haven’t been able to find anything when I knew there should be a universe of prior art to find. Once you stumble on the proper keyword combination, the doorway starts to open.

Even with the best keyword combination, the doorway only starts to open. To do a competent search, you must do more.

For example, once you get manageable results, read the patents and see which ones are relevant. Always remember to try various search terms to ensure you are covering all possible descriptions of the invention.

Along the way, as you read the patents and identify related ones, keep track of the numbers and identify the U.S. classification that relates to the type of invention you are searching. Then, return to the Advanced Search Page and do a classification search.

Again following our example from above, you may notice that classification 206/545 seems relevant to the area of insulated beverage containers. As it turns out, this classification relates to special receptacles or packages with an insulating feature.

Therefore, it would seem that patents within this classification are potentially highly relevant. So, return to the Advanced Search Page text box and enter “CCL/206/545.” This will search for all the patents classified in 206/545—which, as of the time the search was conducted, resulted in 156 U.S. patents.

You can also add to a classification search to narrow. For example, if you search “CCL/206/545 and SPEC/beverage,” you get down to 55 US patents issued since 1976.

Even as the old U.S. classification system becomes obsolete, the same will work with respect to the Cooperative Patent Classification or CPC classes. You would just use “CPC/” and the classification number without the numbers in parenthesis.

Any successful search must use classification searching. Although the classification system is helpful, never forget that patents are classified as the patent office sees fit. In order to identify the appropriate classification, a broad search is necessary to ensure you familiarize yourself with how inventors and patent attorneys routinely characterize certain inventions, features, scientific principles and concepts.

Only after you have a broad idea of all possible descriptions can you meaningfully search the classification systems. Some will disagree with this last statement, though.

Frequently, a patent classification search is the only type of search that is conducted by individuals who are professional patent searchers. It is important to realize, however, that a professional searcher only searches for a living and is far more familiar with the classification system than any inventor or even any patent attorney. If you think you are familiar enough with the classification system, you are not!

It is critically important to figure out what things are called. I cannot stress this enough. You must use different names and labels.

You will find that patent attorneys typically call certain features by a select few names. These names are not always obvious, but once you figure out what the industry calls something you are far more likely to find relevant patents.