Invalidity contentions are the formal disclosure in which the defendant in a US patent suit sets out why the asserted claims are invalid. They are easily confused with the invalidity search, which is the research that finds the prior art. A Rule 11 claim chart belongs to the other side, and it records the infringement analysis that the patent owner makes before suit.
The defendant commissions a patent invalidity search once the patent is known, and defence counsel serves the invalidity contentions on a date set by the court.
The three terms at a glance
| Aspect | Invalidity search | Invalidity contentions | Rule 11 claim chart |
|---|---|---|---|
| What it is | Research that finds prior art | Formal disclosure of invalidity grounds | Record of the pre-filing infringement analysis |
| Prepared by | Patent searcher | Defence counsel, often with charts from a search firm | Counsel for the patent owner |
| Claims are compared with | Earlier patents, literature and products | The prior art relied on | The accused product |
| Timing | As soon as the patent is known | Date in the local patent rules or scheduling order | Usually before the complaint is filed |
The court rules and statutes cited below were checked in October 2026.
What is an invalidity search?
An invalidity search looks for earlier patents and non-patent literature that disclose what the claims of a patent cover. The report ranks the references and maps them to the claim elements, and the guide to the invalidity search process and cost sets out the method.
As a reference point, invalidity searches at Synoptic IP cost USD 1,200–10,000 and take 1–3 weeks (figures checked in October 2026). A related article compares patentability, freedom to operate (FTO) and invalidity searches.
What are invalidity contentions?
Invalidity contentions are a written statement, served by the defendant, of the grounds on which it argues that the asserted claims are invalid. Many US district courts have local patent rules that make both sides disclose their positions early.
Under Patent Local Rule (Patent L.R.) 3-3 of the Northern District of California, they are due not later than 45 days after the defendant is served with the infringement contentions and must contain:
- the identity of each item of prior art;
- whether each item anticipates each asserted claim or renders it obvious;
- a chart that locates each claim limitation in each item of prior art;
- any further grounds, such as indefiniteness, enablement or written description.
Patent L.R. 3-6 allows the contentions to be amended only by order of the court, on a timely showing of good cause. Recently found prior art, despite an earlier diligent search, is one circumstance the rule lists, so a search that started late is hard to repair.
What is a Rule 11 claim chart?
A Rule 11 claim chart compares each element of an asserted claim with the accused product. Counsel for the patent owner usually prepares it before filing suit, and no rule prescribes a format.
The name comes from Rule 11 of the Federal Rules of Civil Procedure, under which an attorney certifies that a complaint’s factual contentions have evidentiary support after a reasonable inquiry. In View Engineering v. Robotic Vision Systems (2000), the Federal Circuit held that counsel must at least apply the claims of each asserted patent to an accused device. The chart is the usual record of that analysis, laid out like an evidence of use chart.
How the three fit together in a case
The work usually follows this order:
- Counsel for the patent owner records the infringement analysis in the Rule 11 claim chart.
- The complaint is served, and under 35 U.S.C. 315 the defendant then has 1 year to petition for inter partes review (IPR).
- The defendant commissions the invalidity search.
- The patent owner serves its infringement contentions.
- The defendant serves its invalidity contentions with the invalidity claim charts.
Invalidity contentions and IPR petitions compared
Under 35 U.S.C. 311, an IPR petition can rely only on patents and printed publications, while invalidity contentions in court can also rely on prior sales and public uses.
What the search firm supplies and what counsel decides
A search firm supplies the search report and invalidity contention claim charts that quote each reference against each claim element. Counsel takes every legal position, including claim construction and the obviousness combinations, and signs and serves the contentions.
Search and chart support for invalidity contentions
Synoptic IP conducts invalidity searches and prepares claim charts for invalidity contentions. To receive a quote and a delivery date, send us the patent numbers, the asserted claims and the contention deadline through our contact page.
This guide is general information and is not legal advice.
Frequently Asked Questions
When are invalidity contentions due?
The date depends on the court. In the Northern District of California, they are due not later than 45 days after service of the infringement contentions (Patent L.R. 3-3, checked in October 2026). Where a court has no patent rules, the judge usually fixes the date in a scheduling order.
Can invalidity contentions be amended after they are served?
Yes, but usually only with the permission of the court. In the Northern District of California, an amendment needs a court order and a timely showing of good cause. The Federal Circuit has held, in O2 Micro v. Monolithic Power Systems, that good cause requires a showing of diligence.
Is a Rule 11 claim chart filed with the complaint?
Not necessarily. Rule 11 requires a reasonable inquiry before filing and does not mention a claim chart. Some patent owners attach one to the complaint, and in districts with patent local rules an infringement chart is served with the infringement contentions.
What is the difference between infringement contentions and invalidity contentions?
Infringement contentions come from the patent owner and map the asserted claims to the accused product. Invalidity contentions come from the defendant and map the same claims to the prior art. In the Northern District of California, the patent owner serves first, under Patent L.R. 3-1.
Does Rule 11 apply to an invalidity defence?
Yes. Rule 11 covers the claims, defences and other legal contentions in a pleading, so an answer that pleads invalidity carries the same certification as a complaint. The term Rule 11 claim chart is still used mainly for the pre-filing infringement chart.