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 three differ in who prepares them and when. Counsel for the patent owner usually prepares a Rule 11 claim chart before the complaint is filed. The defendant commissions a patent invalidity search once the patent is known. Defence counsel then serves the invalidity contentions, supported by invalidity claim charts, 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. The guide to the invalidity search process and cost sets out the method.
The report is working material for counsel, so it is not a court document and is not served on the other side.
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 on the other parties, of the grounds on which it argues that the asserted claims are invalid. Many US district courts have adopted local patent rules that make both sides disclose their positions early. The contentions are the defence side of that exchange.
The Patent Local Rules of the Northern District of California are one example. Under Patent Local Rule (Patent L.R.) 3-3, 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, such as the number, country and issue date of a patent;
- whether each item anticipates each asserted claim or renders it obvious, with any combinations relied on;
- a chart that locates each limitation of each asserted claim in each item of prior art;
- any further grounds, such as patent eligibility, indefiniteness, enablement or written description.
A copy of each item that is not already in the file history of the patent is produced with the contentions. Where an item is not in English, Patent L.R. 3-4 also requires an English translation of the portions relied on.
Why late prior art is hard to add
Patent L.R. 3-6 allows invalidity contentions to be amended only by order of the court, on a timely showing of good cause. Prior art found recently, despite an earlier diligent search, is one circumstance that the rule lists as possible support for good cause. A search that started late or stopped early is therefore 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. The name is informal, and no rule prescribes a format.
The name comes from Rule 11 of the Federal Rules of Civil Procedure. By presenting a complaint to the court, an attorney certifies that its factual contentions have evidentiary support, after an inquiry that is reasonable under the circumstances. A court that finds a violation can sanction the attorney, the law firm or the party.
The Court of Appeals for the Federal Circuit applied this rule to patent cases in View Engineering v. Robotic Vision Systems, decided in 2000. According to that decision, counsel must at least apply the claims of every asserted patent to an accused device and find a reasonable basis for alleging infringement. The rule requires the analysis and does not mention a chart. The chart is the usual record of it, 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 analyses infringement and records the result 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, which identify the asserted claims.
- The defendant serves its invalidity contentions with the invalidity claim charts.
- The court construes the claims.
The following timeline is an illustration and does not describe a real project. In a Northern District of California case, the infringement contentions are served on 2 March and the invalidity contentions are due by 16 April. If the search starts only on 2 March, that period has to cover the search, the review of the results, the charting and the drafting. A search that starts when the complaint arrives leaves more of the period for the charts.
Invalidity contentions and IPR petitions compared
The same search often supports an IPR petition at the United States Patent and Trademark Office (USPTO), although the two filings follow different rules.
Under 35 U.S.C. 311, an IPR petition can rely only on patents and printed publications. Invalidity contentions in court can also rely on prior sales and public uses. Under section 315, the petitioner cannot, after a final written decision, assert in court any ground that it raised or reasonably could have raised in the IPR. A search report that separates the printed publications from the products and systems shows which references can be used both in court and at the USPTO.
What the search firm supplies and what counsel decides
A search firm supplies the factual material, which for invalidity contentions usually means:
- the search report with the ranked references;
- invalidity contention claim charts that quote each reference against each claim element, with the column, line, paragraph or figure cited;
- the publication date of each reference;
- comments that mark a weak or partial mapping.
Counsel takes every legal position, including the proposed claim construction, the asserted references and the obviousness combinations. Counsel also signs and serves the contentions. The cost of the charts depends on the number of asserted claims, the number of references, whether dependent claims are charted and how close the deadline is.
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 under these rules 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, not later than 14 days after the initial case management conference (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.