Patent Strategy · Before You File
How to Do a Prior Art Search
A prior art search tells you whether your invention is novel — and where to draw your claims to avoid what already exists. Here is how to run one, step by step.
Key takeaways
- →Prior art is any public disclosure before your filing date — patents, papers, products, web pages, all count.
- →The USPTO searches regardless — your search is strategic: it helps you decide whether to file and where to draw claims.
- →Search at least four places: USPTO PatFT, Google Patents, Espacenet, and non-patent literature (Google Scholar, IEEE, etc.).
- →A CPC classification search finds art even when terminology differs — more reliable than keywords alone.
- →Everything material you find must be disclosed to the USPTO in an Information Disclosure Statement (IDS).
- →No prior art found ≠ novelty guaranteed. Professional searchers for complex inventions are worth the cost.
What is prior art?
The legal definition under § 102
Under 35 U.S.C. § 102, an invention is patentable only if it is novel — meaning no single prior art reference discloses every element of the claimed invention. “Prior art” means any disclosure that was publicly available before your effective filing date.
That covers US and foreign patents, published patent applications, journal articles, conference papers, product manuals, trade catalogs, on-sale products, publicly-demonstrated technology, and web pages. The disclosure can be in any language, and it can come from anywhere in the world. There is no geographic limit on what counts as prior art.
For US applicants there is a limited one-year grace period: your own disclosures (publications, sales, public demonstrations) made within one year before your filing date do not automatically bar you. But a third party’s independent disclosure of the same invention with no grace period grace — if they published it before your filing date, it is prior art even if you invented it first. This is the core consequence of the first-to-file system.
The novelty test (§ 102): A claimed invention is anticipated if a single prior art document discloses every element of the claim, arranged the same way. If even one claim element is missing from all known prior art, the claim may be novel — but still must clear the non-obviousness hurdle of § 103.
Why search first?
Four reasons before you pay a patent attorney
Reason 1
Avoid wasted spend
A utility patent costs $10,000–$25,000 all-in. Discovering blocking art before you file saves you all of it. If your core concept is already patented, you can pivot your claims, design around the reference, or abandon — without having spent on prosecution.
Reason 2
Write stronger claims
Knowing the closest prior art lets your attorney craft claims that are as broad as possible while still being novel. An application drafted without a search often receives avoidable rejections that require narrowing amendments — which shrink scope permanently.
Reason 3
Satisfy the duty of candor
You are legally required to disclose to the USPTO all information you are aware of that is material to patentability (37 C.F.R. § 1.56). Searching and then filing your IDS simultaneously satisfies this obligation and protects enforceability.
Reason 4
Assess freedom-to-operate
A prior art search and an FTO search overlap but differ. Prior art search asks 'can I patent this?' FTO asks 'can I make and sell this without infringing active patents?' Many founders need both — the search surfaces relevant patents for both questions at once.
The search process
Seven steps, in order
Define your invention in functional terms
Before searching, write three things: (1) what problem does this solve, (2) the essential technical mechanism — not the application, but the underlying principle, and (3) alternative ways someone could achieve the same result. This gives you search terms beyond your product name. An invention described as 'a coffee cup with a lid' is hard to search; 'a beverage container with a resealable aperture seal' finds the relevant CPC codes and prior art.
Build a keyword list with synonyms
Patent claims use highly specific legal language that often differs from engineering or marketing language. Brainstorm synonyms, alternative descriptions, and related concepts. A 'smartphone' might also appear as 'handheld computing device,' 'portable wireless terminal,' or 'mobile station.' Include both narrow (your exact embodiment) and broad (the underlying concept) terms. You will iterate on this list as you find relevant patents and read their claims and abstracts.
Search USPTO PatFT and AppFT
The USPTO Patent Full-Text Database (PatFT) contains all granted US patents since 1976 in full text, and since 1790 in image form. The Application Full-Text Database (AppFT) covers published applications since 2001. Use the Advanced Search at patft.uspto.gov for field-specific queries — TTL (title), ABST (abstract), ACLM (claims), SPEC (specification), ICL (international classification). Example: TTL/resealable AND ABST/aperture. For modern filings, Patent Center (patentcenter.uspto.gov) gives access to the complete file wrapper.
Search Google Patents for keyword sweep
Google Patents (patents.google.com) provides the best natural-language and full-text keyword search across USPTO, EPO, WIPO PCT, and many national offices. Use the Advanced Search to filter by filing date (to find prior art from before your priority date), assignee (to find a competitor's portfolio), or CPC code (to find a technology class). The 'Similar documents' feature on any result surfaces related patents you might have missed with keywords alone.
Search Espacenet and WIPO PATENTSCOPE for international art
Espacenet (worldwide.espacenet.com) covers over 140 million documents from 100+ patent offices — European patents, JP, CN, KR, and more. WIPO PATENTSCOPE (patentscope.wipo.int) indexes PCT applications. Both are critical: a prior-filed EP or JP patent is equally valid prior art for a US application. Use Espacenet's Classification Search to browse CPC codes and find patents in your technology bucket regardless of language — machine translation is built in.
Search non-patent literature (the trap most inventors miss)
Prior art is not limited to patents. Any printed publication anywhere in the world — academic papers, conference proceedings, technical standards, product manuals, catalogs, datasheets, blog posts, forum threads — qualifies as prior art if it was publicly available before your filing date. Search Google Scholar, IEEE Xplore, PubMed (for biotech), arXiv, and industry-specific databases. Trade publications, product launch announcements, and even archived web pages (via the Wayback Machine) can all be prior art.
Analyze, document, and decide
For each reference you find, ask: does any single prior art document disclose every element of my proposed broadest claim? If yes, that claim as written is anticipated (§102-rejected). Do two or more references together cover all elements in a way an ordinary skilled person would combine? If yes, it's obvious (§103). Document every reference you found — this becomes your IDS list. If you find no blocking art, that is evidence of patentability, not certainty.
Where to search
The four essential databases
Use all four. Each database has different coverage. Stopping at one means missing prior art that could invalidate your patent years later.
USPTO PatFT / AppFT
patft.uspto.gov
Covers: All US granted patents (1976+) and published applications (2001+)
Best for: Field-specific queries: claims, title, assignee, classification
Limitation: US only; no natural-language search
Google Patents
patents.google.com
Covers: 110M+ documents from USPTO, EPO, WIPO, JP, CN, KR, DE, and more
Best for: Natural-language and keyword search; machine translation; Similar Documents
Limitation: Slight lag on newest filings; not all NPL indexed
Espacenet (EPO)
worldwide.espacenet.com
Covers: 140M+ documents from 100+ patent offices
Best for: CPC classification browser; EP and PCT documents; built-in translation
Limitation: Search interface less intuitive than Google Patents
WIPO PATENTSCOPE
patentscope.wipo.int
Covers: PCT international applications and national collections from member states
Best for: Cross-lingual expansion; sequence listings; chemical structures
Limitation: Best for PCT; national office coverage varies
Don’t skip non-patent literature
Academic papers, conference presentations, technical standards (IEEE, IETF RFCs, ISO documents), product manuals, and archived web pages all count as prior art. For software and biotech inventions, non-patent literature is often the most relevant prior art. Search Google Scholar, IEEE Xplore, PubMed (biotech), arXiv (CS/physics/math), and ACM Digital Library. Use the Wayback Machine (web.archive.org) to establish when a web page was publicly available.
Search strategy
CPC classification search: the underused technique
Most inventors search by keywords. Examiners search by classification. A classification search is more thorough because it finds patents even when the inventors used completely different terminology for the same concept.
The Cooperative Patent Classification (CPC) system is a joint USPTO–EPO taxonomy with ~250,000 classification codes organized hierarchically. Every patent is assigned one or more CPC codes at examination.
How to find your CPC code
- Find any patent in your technology area (e.g., search Google Patents for a known competitor product).
- Open that patent and look at the 'Classifications' section — you will see one or more CPC codes like H04W 72/04.
- Click that code (in Google Patents) or enter it in Espacenet's Classification Search to see the full taxonomy tree and all patents in that bucket.
- Scan the surrounding codes (siblings and parents in the hierarchy) to find adjacent technology buckets you might have missed.
- Run a PatFT Advanced Search using the IPC field: IPC/H04W72 to pull all matching patents.
A thorough search combines keyword and classification. Start with keywords to find a few relevant patents, extract their CPC codes, then search those codes to find everything the examiner would find.
DIY vs. professional
When to hire a professional searcher
A DIY search on Google Patents takes 1–2 hours and costs nothing. A professional prior art search costs $500–$2,000 and takes 2–5 business days. The decision depends on what is at stake.
DIY is fine when:
- The invention is straightforward and narrowly defined
- You want a quick sanity check before engaging an attorney
- The technology is well-documented in English-language patents
- Budget is extremely limited (early-stage idea, not committed to filing)
Hire a professional when:
- The technology is complex, highly technical, or cross-disciplinary
- Significant investment ($50k+) depends on patentability
- The invention touches heavily non-patent-literature fields (chemistry, biotech, software prior to 2001)
- You need a defensible search for due diligence (investors, acquirers)
Note: A searcher’s job is to find prior art — they do not give legal opinions on patentability. That analysis (and the IDS filing) is done by a registered patent practitioner.
After the search
Disclosing what you find: the IDS
Once you file, you must disclose to the USPTO all prior art you are aware of that is material to patentability. This is done via an Information Disclosure Statement (IDS), filed using USPTO Form PTO/SB/08. You can file an IDS for free before the first Office Action, and with a small fee up to payment of the issue fee.
The IDS lists each reference — patent number (for patents), full citation (for papers) — and you must provide a copy of each non-patent reference unless it is already in the USPTO’s database. The examiner reviews the listed art and stamps each reference initialed to confirm it was considered.
Failure to disclose material prior art you knew about is inequitable conduct — a defense that can render a patent unenforceable in litigation even if the patent is otherwise valid. Examiners are not penalized for allowing over disclosures but can invalidate patents for withheld ones. When in doubt, disclose.
FAQ
Common questions
What counts as prior art for a patent?
Under 35 U.S.C. § 102, prior art is any patent, published patent application, printed publication, public use, on-sale activity, or other public disclosure that was available before the effective filing date of your application. This includes foreign patents, academic papers, product manuals, trade-show demonstrations, your own prior publications, and even unrecorded public uses. For US applicants, there is a one-year grace period for your own disclosures, but third-party disclosures are absolute prior art.
How thorough does a prior art search need to be?
The USPTO conducts its own search regardless of what you submit, so the purpose of your search is strategic, not mandatory. A thorough search helps you decide whether to file at all, refine your claims to avoid the closest art, and identify what you must disclose under the duty of candor (37 C.F.R. § 1.56). Professional searchers typically spend 4–10 hours and charge $500–$2,000 for a utility patent search. DIY searches on Google Patents and USPTO PatFT can surface obvious blocking art in 1–2 hours for free.
Can I use Google Patents for prior art search?
Yes. Google Patents indexes USPTO, EPO, WIPO, and many national offices — it is the best free tool for keyword-based patent searching. Its strengths are natural-language search and translation of foreign-language patents. Its weakness is that it does not always index the most recent publications (there can be a few days' lag) and it does not index all non-patent literature. Use it alongside USPTO Patent Center for status and Espacenet for EP/WO documents.
What is a CPC classification search and why does it matter?
The Cooperative Patent Classification (CPC) is a joint USPTO–EPO hierarchical system that groups patents by technology. A classification search finds all patents in the same technology bucket — even those with different vocabulary than yours. It is often more reliable than keyword search because inventors use different words for the same concept. You can find the CPC code for your technology by looking up a known patent in your field and reading its classification codes, then searching that code in PatFT or Google Patents.
Do I have to disclose prior art I find to the USPTO?
Yes. Under 37 C.F.R. § 1.56 (the duty of candor), you must disclose all information material to patentability that you are aware of. This is done via an Information Disclosure Statement (IDS). Failure to disclose material prior art you knew about is inequitable conduct — a defense that can render a patent unenforceable even if valid. Disclosing art does not mean your application will be rejected; the examiner decides whether it is actually relevant.