A patent infringement claim chart maps every limitation of an asserted patent claim, in the left column, to the specific feature of the accused product that allegedly embodies it, in the right column, with cited evidence for each match. Build it by selecting the right claims, choosing a theory of infringement for each limitation, gathering evidence that supports every row, and serving it on the schedule the court’s local patent rules require. A chart that leaves even one limitation unmatched gives the defendant a clean path to summary judgment on that claim.
What the Chart Has to Show
A patent protects specific claims, and each claim is made up of individual elements called limitations that define the boundaries of the invention. An accused product literally infringes a claim only if it contains each and every limitation recited in that claim.1World Intellectual Property Organization. WIPO Patent Judicial Guide – United States – Section 10.5 The chart’s job is to prove that element-by-element match on paper.
The format is two columns. The left column reproduces the exact language of each asserted claim, broken into its individual limitations. The right column describes the specific feature, component, or behavior of the accused product that corresponds to each limitation, supported by citations to evidence: excerpts from technical manuals, screenshots of product interfaces, API documentation, or source code references. A judge or jury should be able to read across any row and see why the claimed element is present in the accused product without needing an engineering background.
If a single limitation has no match in the accused product, the infringement allegation for that claim collapses. That is where weak cases usually reveal themselves, in the quiet work of preparing the chart rather than in the courtroom.
Choosing Which Claims to Chart
A patent can contain dozens of claims, and charting all of them against an accused product is rarely practical or strategically wise. Claim selection is one of the most consequential decisions in building the chart.
Independent claims stand on their own and define the broadest version of the invention. Dependent claims incorporate every limitation of the claim they depend on and add further restrictions. Because a dependent claim includes everything in its parent, if the accused product does not infringe the independent claim it cannot infringe anything that depends on it. Infringement analysis therefore starts with the independent claims; a dependent claim is worth charting only after the parent has a solid match.
The strongest chart focuses on the claims whose limitations most closely align with the accused product’s features and whose matches are supported by the most accessible evidence. Charting too many claims dilutes the presentation and exposes weak rows. Charting too few leaves stronger theories on the table. A common approach is a core set of independent claims plus a handful of dependent claims that add commercially significant limitations, the kind of features a defendant would find hardest to design around.
Literal Infringement or Doctrine of Equivalents
Every row of the chart has to specify the theory of infringement, and the choice changes what the row needs to show.
Literal infringement is the simpler case: the accused product contains a feature that directly matches the claim language. If the claim requires “a rotating drum with a diameter of at least six inches” and the product has a rotating drum with a seven-inch diameter, that limitation is literally present. The row identifies where and how the feature appears, and cites the evidence.
The doctrine of equivalents reaches features that do not literally match the claim language but achieve the same result through an insubstantial variation. The Supreme Court has held that this analysis must be applied limitation by limitation, not to the invention as a whole, so that the doctrine does not swallow the patent’s boundaries.2Justia Law. Warner-Jenkinson Co Inc v Hilton Davis Chemical Co, 520 US 17 (1997) For each limitation asserted under equivalents, the chart has to show that the accused feature performs substantially the same function, in substantially the same way, to achieve substantially the same result as the patented element.3Cornell Law School. Doctrine of Equivalents That is three distinct showings, and each needs its own explanation and support.
One trap closes off equivalents before the chart is even written: prosecution history estoppel. If the patent holder narrowed a claim during prosecution to get the patent allowed, the holder generally cannot use the doctrine of equivalents to recapture the surrendered territory. Reviewing the prosecution history before deciding which theory to assert for each limitation is essential; an equivalents argument that runs into an amendment buried in the file wrapper does not survive long.
Gathering the Evidence
The Prosecution History
The prosecution history, sometimes called the file wrapper, is the full record of communications between the applicant and the USPTO examiner during the patent’s examination. It includes every amendment to the claims, every argument about patentability, and every reference the examiner cited. It is publicly available through the USPTO.
Reading it serves two purposes. It reveals the intended scope of each claim, including narrowing amendments that limit how broadly the claims can be interpreted. And it flags statements that may trigger prosecution history estoppel. Skipping this step is one of the fastest ways to build a chart that falls apart at claim construction.
The Accused Product
The right column requires deep familiarity with the accused technology. Collect user manuals, technical specifications, white papers, marketing materials, and any published documentation describing how the product works. If the product is commercially available, buying a unit for teardown or testing often reveals internal components, circuit layouts, or mechanical configurations that no document captures but that confirm or disprove a claim match.
Software patents raise a particular problem. When the theory depends on how code operates rather than what a user sees on screen, access to source code becomes essential. Because source code is typically a company’s most closely guarded asset, courts control access through protective orders. Under common default arrangements, source code is loaded onto a password-protected, standalone computer at a neutral location, accessible only to a small number of designated outside attorneys and experts, with no printouts allowed. The reviewer often has to draft the right column from memory and contemporaneous notes, which makes disciplined documentation during the review session critical.
Working With a Technical Expert
A claim chart is only as strong as the technical analysis behind it. Attorneys draft the legal framework, but technical experts supply the substantive link between claim language and product reality. They analyze each claim element, examine the accused product or process, and determine whether the specific limitations are present.
Their most valuable contribution is often translation. Patent claims are written in dense technical language, and accused products carry their own specialized vocabulary. The expert explains in accessible terms why a particular software algorithm corresponds to a claimed “processing module,” or why a mechanical assembly satisfies a claimed “coupling mechanism.” That translation is what makes a chart persuasive to a judge or jury without an engineering background.
Experts also carry the chart forward. They testify at claim construction, summary judgment, and trial. A chart built without meaningful expert involvement often reads as superficial matching of buzzwords, and opposing counsel will expose that on cross-examination.
Direct and Indirect Infringement
Direct infringement covers making, using, selling, or importing the patented invention without authorization during the patent’s term.4Office of the Law Revision Counsel. Title 35 USC 271 – Infringement of Patent A direct infringement chart does the limitation-to-feature mapping described above and nothing more.
Indirect infringement reaches companies that do not themselves practice the invention but either sell a component designed for use in the patented combination or actively encourage others to infringe. Federal law imposes liability for both induced and contributory infringement.4Office of the Law Revision Counsel. Title 35 USC 271 – Infringement of Patent Charting it is a layered exercise. The chart must first identify the underlying direct infringement, naming who is practicing the patented invention and how. It must then describe the accused indirect infringer’s specific acts that contribute to or induce that direct infringement.5United States District Court. Patent Local Rules – Northern District of California For contributory infringement, the chart also has to establish that the component sold is a material part of the invention, was especially made for the infringing use, and has no substantial noninfringing use.
Deadlines and What Has to Be Served
Many federal district courts have adopted local patent rules that dictate when and how claim charts are served. The rules vary, but most follow a framework modeled on the Northern District of California’s patent local rules, which the Federal Circuit Bar Association used as a template for its model rules.
Under that framework, the party alleging infringement must serve its Disclosure of Asserted Claims and Infringement Contentions no later than 14 days after the initial case management conference.5United States District Court. Patent Local Rules – Northern District of California The disclosure has to include:
- Each asserted claim of each patent asserted against each defendant, with the applicable subsection of the infringement statute.
- Each accused product, device, process, or method, identified by name or model number.
- An element-by-element chart showing where and how each limitation of each asserted claim is found in the accused product.
- Whether each limitation is alleged to be literally present or present under the doctrine of equivalents.
- For indirect infringement claims, identification of the direct infringement and the accused indirect infringer’s role.
- The point of first infringement and the start and end of claimed damages.
Deadlines in other districts differ, so check the local patent rules for the court where the case sits before you build the schedule.
Amending the Chart Later
Infringement contentions are not meant to be living documents. Once served, they can generally be amended only with leave of court on a timely showing of good cause. Courts evaluate good cause mainly by looking at diligence, meaning whether the party discovered the basis for the amendment promptly and sought the change without unnecessary delay.
Circumstances that typically support good cause include learning nonpublic information about the accused product that was not available before the original contentions were served. Courts also weigh whether the opposing party would be unfairly prejudiced and whether the request looks like gamesmanship.
The most common trigger for amendment is a claim construction ruling. After the court interprets disputed claim terms at a Markman hearing, the adopted constructions may shift which limitations match the accused product. Most courts allow some opportunity to update contentions in response, though the timelines and procedures vary by district. Waiting until after Markman to notice obvious problems in the original chart will not satisfy the diligence requirement; the court expects the initial contentions to reflect reasonable pre-filing analysis.
What a Weak Chart Costs
Courts take the quality of infringement contentions seriously. Missing a single claim limitation leaves the infringement allegation vulnerable to dismissal on summary judgment. Filing contentions late or failing to comply with the local patent rules can draw sanctions, up to and including having specific claims stricken from the case.
The consequences reach further than local rules. Federal courts have imposed sanctions under Rule 11 when a party filed infringement claims without a reasonable prefiling investigation, including cases where the plaintiff made no attempt to obtain a sample of the accused product, conducted no independent infringement analysis, and performed no reverse engineering or review of technical specifications. In one case before the International Trade Commission, an administrative law judge imposed a $1 million sanction against a complainant that had performed no claim construction on its patent before filing.
The practical lesson is simple. The claim chart is the single document most likely to determine whether a patent case survives its first year. Thorough technical analysis, careful claim selection, and precise evidence mapping at the charting stage pay off at every later phase. Cutting corners here does not save time; it creates problems that compound as the case moves forward.