A prior art search is a structured search of patents and other publications for earlier disclosures that bear on whether an invention is new and inventive. A trained searcher turns the invention into key features, searches patent and non-patent sources, and reports the closest references with a feature-by-feature comparison that an attorney can act on.
Attorneys commission one before filing an application, when a granted patent has to be challenged, and when a team needs to know what a field already contains. This guide sets out the method a professional prior art search service follows, the report it produces, its limits and its cost.
What counts as prior art
Under 35 U.S.C. 102(a)(1), an invention cannot be patented if it was “patented, described in a printed publication, or in public use, on sale, or otherwise available to the public” before its effective filing date. A US patent or published US or international application that names another inventor and was effectively filed earlier also counts, under section 102(a)(2).
The US allows a 1-year grace period for the inventor’s own disclosures, but Europe is stricter. Article 54(2) of the European Patent Convention treats everything made available to the public before the filing or priority date as part of the state of the art. Article 55 allows only narrow exceptions, such as evident abuse in the 6 months before filing.
Prior art has no language or format requirement. Each of the following can qualify if it was publicly accessible in time:
- a Japanese utility model or a Chinese patent application;
- a conference poster or slide deck;
- a university thesis;
- a product manual, datasheet or archived web page.
Types of prior art search
| Search type | When it is done | Date that matters | Use of the result |
|---|---|---|---|
| Patentability (novelty) | Before filing | Planned filing date | Filing decision and claim drafting |
| Invalidity | After grant: litigation, inter partes review, opposition | Priority date of the target patent | Challenging granted claims |
| State of the art | Before research or investment | None | Known solutions and gaps |
The patent invalidity search has its own guide. A freedom to operate (FTO) search is different again: it reads the claims of patents in force, as the FTO search guide explains.
How professionals carry out a prior art search
A professional search usually runs through 5 stages, in a similar order in most technologies.
- Key features. The searcher splits the invention into features and agrees them with the attorney.
- Classification. Cooperative Patent Classification (CPC) groups are chosen, so that documents with unexpected wording are still found.
- Search strings. Keywords, synonyms, truncation and proximity operators are combined with the classes and refined as new terms appear.
- Citations and families. Citations to and from the closest documents are checked, along with their family members.
- Screening and mapping. Hits are screened, read in full and mapped against each feature.
Patent databases cover only part of the published record. A non-patent literature search covers journals, theses and product documents, and a foreign language search covers Chinese, Japanese and Korean records. Free tools include Espacenet and the Patent Public Search tool of the United States Patent and Trademark Office (USPTO). It remains free, but from 7 November 2026 users must sign in with a USPTO account.
What you receive: the patent search report
A professional patent search report usually contains the following parts:
- the scope, date cut-off and databases;
- the search strategy, with classes and strings;
- a ranked list of the closest references;
- a feature-by-feature mapping with cited passages;
- a summary of which features appear to be disclosed.
The strategy section lets an attorney judge whether a gap in the results reflects the art or the search.
The 18-month blind spot in every prior art search
No search can find applications that have not yet been published. Under 35 U.S.C. 122(b), US applications are generally published promptly after 18 months from the earliest filing date. An applicant can also ask, on filing, for no publication at all, if the invention will not be the subject of a foreign or international application that requires 18-month publication.
An application filed in that window still becomes prior art against a later one once it publishes, as of its effective filing date. A repeat search 18 months later closes part of the gap.
Search cost and turnaround
Cost depends on the number of features, the technology, the languages and the depth of the mapping. Synoptic IP publishes these ranges (checked October 2026):
- patentability search: USD 150–1,200, in 2–10 business days;
- invalidity search: USD 1,200–10,000, in 1–3 weeks.
Commissioning a prior art search
If you have an invention or a granted patent to test, our team can scope a prior art search and send a proposal through our patentability search page.
This guide is general information and is not legal advice.
Frequently Asked Questions
What is the difference between prior art search and patentability search?
A patentability search is one type of prior art search. Prior art search is the wider term and also covers invalidity and state-of-the-art work. A patentability search, also called a novelty search, tests a planned invention against everything published before the intended filing date.
How long is a prior art search valid?
A prior art search reflects the published record on its search date and nothing later. Applications filed in the previous 18 months may still be unpublished, and new documents appear constantly. A repeat search shortly before filing, or before a step in litigation, picks up what the first search could not see.
Can I search for prior art myself for free?
Yes, a basic search is possible with free tools such as Espacenet, Google Patents and Patent Public Search. It is useful as a first look, but a self-search often misses documents that use different wording, sit in other classes or exist only in another language.
Does prior art have to be in English?
No, a document in any language counts if it was available to the public before the relevant date. Chinese, Japanese, Korean and German documents often appear in professional search results, and the searcher reads them in machine translation or with a native speaker.
Is a search required before filing a patent application?
No, US law does not require an applicant to search before filing. However, under 37 CFR 1.56, inventors, attorneys and others substantively involved in a US application must disclose information they know to be material to patentability, usually through an information disclosure statement.