If a patent claim is the law of the case, a claim chart is where the plaintiff actually has to show their work. The complaint tells a story. The claim chart maps every word of the asserted claim, line by line, onto something the defendant allegedly does. It is the homework. And on a troll case, the homework is usually rushed.
A claim chart is also where most defendants stop reading and start panicking. Don't. A chart that looks intimidating in 12-point Times New Roman often falls apart the moment you ask whether each cited piece of "evidence" actually shows what the claim requires. This article is how to read one without flinching.
What a claim chart IS
A claim chart is an element-by-element mapping from a single patent claim to a single accused product. Two columns:
| Claim language (left) | Alleged infringement evidence (right) |
|---|---|
| Each limitation of the claim, broken out as its own row | A screenshot, code snippet, spec citation, marketing copy, or other artifact that supposedly shows the accused product meeting that limitation |
The plaintiff has to do this for every limitation of every asserted claim. Miss one, and there's no infringement of that claim. That's the rule from Warner-Jenkinson Co. v. Hilton Davis Chemical and a hundred Federal Circuit cases since: literal infringement requires that every element of the claim be present in the accused product. Not the gist. Not most of them. Every one.
Charts show up in three places:
- Demand letters — sometimes attached, often summarized in prose. The thinner version. Plaintiffs hold back detail to keep optionality.
- Complaints — Federal Rule 8 plausibility plus Iqbal / Twombly increasingly forces plaintiffs to include claim charts as exhibits to survive a Rule 12(b)(6) motion.
- Preliminary infringement contentions — required by local patent rules in N.D. Cal., E.D. Tex., D. Del., and most other patent-heavy districts. These are the real claim charts. They get amended, but only with court permission. They are the contentions the plaintiff actually has to win on.
A claim chart is not a court order. It's the plaintiff's argument about what the claim covers and what your product does. Both halves of the chart are contestable.
What a claim chart isn't
Three things people assume claim charts are, and they aren't:
- They aren't a finding of infringement. A chart is one party's allegation. The court hasn't construed a single term. No discovery has happened. The chart is opening argument, not verdict.
- They aren't claim construction. What a claim term means is decided at a Markman hearing, often a year into the case. A plaintiff's chart applies the plaintiff's interpretation of every claim term. You get to fight that.
- They aren't proof that the plaintiff did the work. Some charts are filled out by patent examiners, some by senior litigators, some by junior associates with a 48-hour deadline and a screenshot tool. The quality varies wildly. The signature on the complaint binds the lawyer to Rule 11 — but only if you make the court care.
Limitations: why every row matters
The rows of a claim chart correspond to limitations — the discrete requirements a claim imposes. A claim that reads:
A method comprising: (a) receiving a query from a user; (b) parsing the query into tokens; (c) ranking results based on token frequency; (d) presenting the ranked results in a paginated interface.
…has at least four limitations. Some patent courts split them further (the "parsing" step itself often has sub-elements). A complete claim chart has a row for each one, and the right-hand column has to demonstrate that the accused product does that specific thing.
If the plaintiff's "ranking results based on token frequency" row shows a screenshot of your search results page, that's not evidence. That's a picture of an output. The chart has to demonstrate the mechanism — that your system actually computes a ranking based on token frequency, not that the page renders sorted results. This distinction kills more weak charts than any other single defense.
The mental model: each row is an independent attack surface. To win, the plaintiff needs every row. To win non-infringement, you need one row to fall.
The thinness signals
Most NPE claim charts are thinner than they look. Things to look for, in roughly the order you'll spot them on a first read:
flowchart TD
START["New claim chart in hand"] --> READ["Read the claim<br/>without looking at the chart"]
READ --> ID["Identify the limitations<br/>(number them)"]
ID --> ROW["For each row, ask 4 questions"]
ROW --> Q1{"Is the cited evidence<br/>about THIS limitation?"}
ROW --> Q2{"Does the evidence show<br/>the mechanism, not just output?"}
ROW --> Q3{"Are different rows<br/>citing the same source?"}
ROW --> Q4{"Is anything 'assumed'<br/>or 'on information and belief'?"}
Q1 -->|"No"| FLAG["Flag: mismatched citation"]
Q2 -->|"No"| FLAG2["Flag: output-not-mechanism"]
Q3 -->|"Yes (one URL repeats)"| FLAG3["Flag: single-source chart"]
Q4 -->|"Yes"| FLAG4["Flag: assumed-not-shown"]
FLAG --> SCORE["Count flags"]
FLAG2 --> SCORE
FLAG3 --> SCORE
FLAG4 --> SCORE
SCORE --> POSTURE{"Many flags?"}
POSTURE -->|"Yes"| RULE11["Rule 11 / § 285 territory<br/>+ motion to dismiss"]
POSTURE -->|"A few"| LEVERAGE["Non-infringement leverage<br/>for settlement"]
POSTURE -->|"None"| REAL["Plaintiff did real work<br/>focus on invalidity"]
style START fill:#fff7ed,stroke:#c2410c,color:#1c1917
style RULE11 fill:#fee2e2,stroke:#be123c,color:#1c1917
style LEVERAGE fill:#dbeafe,stroke:#1e40af,color:#1c1917
style REAL fill:#d1fae5,stroke:#047857,color:#1c1917
1. Vague mappings
The cell on the right hand-waves. Phrases that should make you sit up:
- "The accused product includes functionality that…"
- "On information and belief, the system performs…"
- "As shown in Exhibit B, the product generally…"
Vague mappings hide missing analysis. If the plaintiff can't say what specific code path or what specific feature meets the limitation, they probably haven't found one. ("On information and belief" is litigation-speak for "we're guessing.")
2. Missing limitations
Read the claim. Number the limitations. Now look at the chart and check that each numbered limitation has a row. Sometimes plaintiffs collapse two limitations into one row, sometimes skip a limitation entirely on the assumption no one will notice. If a claim has eight limitations and the chart has six rows, you've already won non-infringement — they just don't know it yet.
This sounds too obvious to be a real defense. It is a real defense. It happens regularly.
3. Single-source citations
A chart where every row's right-hand column cites the same URL — usually the accused product's marketing page — is a chart written without looking at the product. Marketing pages are written by marketing. They describe what a product is for, not what it does. Single-source charts are a near-certain sign the plaintiff hasn't done any technical analysis at all.
4. Assumed-not-shown
Watch for steps the plaintiff alleges must happen based on what the output looks like. The mathematical version is: "the output is sorted, therefore the system computes a similarity score, therefore the limitation 'computing a similarity score' is met." Each "therefore" is doing real work and none of it is evidence. (The Lumen View case turned partly on exactly this kind of assumption — the plaintiff alleged a multilateral matching algorithm purely from how the output looked.)
5. Output evidence for mechanism limitations
A claim that requires "computing X" is a process limitation. A screenshot of an interface that displays X is not evidence the system computed it. Maybe a human typed it in. Maybe a third-party API returned it. The chart needs to show the computation, not the result.
6. Doctrine-of-equivalents fallback
If a row says the accused product meets a limitation "literally or, alternatively, under the doctrine of equivalents," the plaintiff is hedging. The doctrine of equivalents lets a plaintiff argue that a non-literal mismatch is "insubstantial." It's a fallback, and it's narrower than it looks: prosecution history estoppel (Festo v. Shoketsu) bars equivalents over subject matter the applicant surrendered during prosecution to get the patent allowed. Look at the file history. If the patentee narrowed a limitation during prosecution, they probably can't recapture it through equivalents.
The Rule 11 problem
Federal Rule 11 requires that lawyers conduct a "reasonable inquiry" before filing — including that infringement contentions have factual support. View Engineering v. Robotic Vision Systems (Fed. Cir. 2000) and a string of subsequent cases say that for patent infringement, "reasonable inquiry" means an element-by-element analysis comparing the accused product to each claim limitation before filing.
A claim chart written from a marketing page, without any look at how the product actually works, is the textbook fact pattern for a Rule 11 violation. So is a chart that asserts infringement of a claim whose plain language obviously doesn't read on the accused product.
Rule 11 sanctions are rare but real. More important, § 285 (fee-shifting under Octane Fitness) uses a lower standard than Rule 11 and lets the prevailing party recover attorney fees in "exceptional" cases. A chart that's transparently thin contributes directly to a later exceptional-case finding. The 2014 Lumen View v. FindTheBest fee award was driven in part by exactly this: a claim chart that asserted multilateral preference matching against a product that did unilateral comparison-based ranking. The court called it sanctionable.
The practical implication: a thin chart is not just a weak case. It is a piece of evidence that the case itself is weak — preserved in writing, signed by counsel, filed on the docket. Save it. You will refer back to it.
Thin on purpose vs. thin by accident
There are two reasons a chart can be thin, and the response differs:
flowchart LR
CHART["Thin chart"] --> WHY{"Why is it thin?"}
WHY -->|"Settlement pressure:<br/>plaintiff filing on volume,<br/>hoping for $50k-$200k payouts"| VOLUME["Treat as bluff<br/>Push back hard<br/>Demand specifics<br/>Threaten § 285"]
WHY -->|"Sloppy lawyering:<br/>real claim, lazy chart"| SLOPPY["Fix the chart in discovery<br/>Don't celebrate too early<br/>Plaintiff can amend"]
WHY -->|"Patent is genuinely<br/>broad / abstract"| ABSTRACT["This is a § 101<br/>Alice problem<br/>File Rule 12(b)(6)"]
style VOLUME fill:#fee2e2,stroke:#be123c,color:#1c1917
style SLOPPY fill:#fff7ed,stroke:#c2410c,color:#1c1917
style ABSTRACT fill:#dbeafe,stroke:#1e40af,color:#1c1917
The intentionally thin chart is a feature of the troll business model. It costs the plaintiff almost nothing to copy-paste a chart across 50 defendants. The math works if even 10% pay $100k to make the case go away. The chart isn't supposed to win at trial — it's supposed to be expensive enough to defend against that paying looks rational.
The accidentally thin chart is a real claim filed by someone who didn't budget for the work. These charts get amended during contentions — local patent rules allow it for good cause. Don't assume the chart you read today is the one you'll be answering at Markman.
The abstract-claim chart is thin because the claim is thin. Software patents that recite generic computer steps tend to produce charts where every limitation maps to "the accused product runs on a computer." Those are Alice cases — file a Rule 12(b)(6) motion on § 101 before you spend a dollar on infringement discovery.
Photo / screenshot vs. spec-citation evidence
The right-hand column of a claim chart can cite different kinds of evidence. Quality varies enormously:
| Evidence type | Quality | Notes |
|---|---|---|
| Source code excerpt | Highest | Hard to get pre-suit (would require leak or open source). Strong signal plaintiff did real homework. |
| API documentation | High | Shows actual behavior, with citations to vendor's own technical writing. |
| Engineering blog post | Medium-high | Often candid about implementation. Defendants' own blog posts are routinely cited against them. |
| Technical spec / RFC | Medium | Shows what the product should do, not what it does. |
| Marketing page screenshot | Low | Describes capability, not mechanism. |
| Product screenshot (UI) | Low | Shows output, not process. Almost never enough on its own. |
| Reviewer / journalist article | Low | Hearsay-adjacent. Useful for context, weak as proof. |
The first thing to do with any chart: count what evidence types show up. A chart that's 100% UI screenshots and marketing copy almost certainly hasn't been near the accused product. A chart with API docs and source-code excerpts means someone did work. That's information about how seriously to take the entire case.
Doctrine of equivalents traps
A few traps that catch defendants who think they've won on non-infringement:
- The "insubstantial difference" argument. Even if a limitation is missing literally, the plaintiff can argue an equivalent is present. The test: would a person of ordinary skill have viewed the accused element as substantially the same? Not "would have known the substitution was possible" — would have viewed them as the same. A high bar, but not zero.
- All-elements rule. Equivalents still apply element-by-element, not to the claim as a whole. The plaintiff can't argue the accused product is "overall equivalent" — they have to map each missing limitation to a specific equivalent in the product.
- Prosecution history estoppel. (Festo.) If the patentee narrowed a claim during prosecution to overcome prior art, they generally surrendered equivalents in the narrowed range. Read the file history before you celebrate a non-infringement read — you want to know which limitations are protected by prosecution history estoppel because the plaintiff can't recapture them.
- The "vitiation" doctrine. Equivalents can't read a limitation out of the claim. If "vertical" is a limitation, "horizontal" can't be equivalent — that would vitiate the limitation. Useful when the plaintiff's equivalents argument essentially rewrites the claim.
A defendant analyzing a chart should mark each limitation as: literally present, literally absent (no equivalents argument), literally absent (equivalents possible), literally absent (equivalents barred by prosecution history). The last bucket is the most valuable. Equivalents barred at the door is the cleanest non-infringement.
Converting a thin chart into leverage
A thin chart isn't just a defense — it's a tool. Three ways to convert it into pressure:
1. Motion to dismiss (Rule 12(b)(6))
Post-Iqbal / Twombly, infringement allegations have to be "plausible," not just possible. A claim chart with vague mappings, missing limitations, or single-source citations is a textbook implausible pleading. Federal Circuit decisions like Disc Disease Solutions v. VGH Solutions and Bot M8 v. Sony have rejected complaints (and dismissed them) for failing to allege element-by-element correspondence.
A Rule 12 motion is not a sure thing — pleading-stage dismissals are case-specific. But filing one is cheap relative to discovery and forces the plaintiff to either amend the chart with real analysis or fight a dismissal motion that highlights every weakness. Either outcome is good.
2. § 285 letter
A pre-answer letter to opposing counsel laying out the chart's defects, citing Octane Fitness / Lumen View, and reserving § 285 rights does two things:
- It puts the plaintiff on written notice. The longer they prosecute a transparently weak case after notice, the harder it is to argue the case wasn't "exceptional."
- It signals you've actually read the chart. A surprising number of trolls drop cases at this point — the math doesn't work if the target has counsel willing to fight.
3. IPR petition
A thin chart is sometimes diagnostic of a broad claim. Broad claims are often invalidated by prior art. If the chart maps everything to "marketing page, generic," the claim is probably broad enough that prior art exists. (Where to start the search →.) An IPR petition filed within the one-year bar ports the fight to the PTAB and often stays the district-court case.
These three tools work together. A motion to dismiss tells the court the chart is thin. A § 285 letter tells opposing counsel you're tracking it. An IPR petition tells the world the claim itself is suspect. None of them require winning at trial. All of them shift the math.
A practical reading checklist
When a new chart lands on your desk:
- Read the claim first, without looking at the chart. Number the limitations. Write what you think each limitation requires.
- Compare your numbering to the chart's rows. Missing rows? Combined rows? Note them.
- For each row, read only the right-hand cell. Does it actually address this limitation, or is it about something adjacent?
- Mark every "on information and belief," "comprises functionality that," and "as shown in Exhibit X." These are hand-waves.
- Tally evidence types. Source code, docs, blogs vs. marketing pages, screenshots, third-party reviews.
- Identify the doctrine-of-equivalents fallbacks. Pull the file history. Are any of them barred by prosecution history estoppel?
- Pick the weakest limitation. That's where your non-infringement story starts.
- Pick the broadest limitation. That's where your invalidity story starts.
Two hours, no money spent, before counsel touches it. The work doesn't replace a litigator's analysis — it makes the litigator's first hour much more productive.
Bottom line
Claim charts are the plaintiff's best opportunity to make infringement look obvious and inevitable. Most of them, on a careful read, are nothing of the sort. The patterns are repetitive: vague mappings, missing limitations, single-source citations, output evidence for mechanism limitations, doctrine-of-equivalents fallbacks that don't survive the file history.
A thin claim chart doesn't just lose at trial. It loses on the docket, in a motion to dismiss, in a § 285 fee-shift letter, in an IPR petition that tells the PTAB the claim is overbroad. The chart is evidence — not just of infringement, but of how seriously the plaintiff is taking the case.
If a chart showed up with your demand letter, the analyzer tears through it row by row in about a minute. If a chart showed up with a complaint, your first 30 days include a careful read and a Rule 12 decision. If you're earlier than that and just trying to figure out what kind of trouble you have, take the quiz.
The plaintiff's leverage in a chart is your willingness to take it at face value. Read it slowly. Number the rows. Most of them don't survive.
This article is for general education and is not legal advice. Claim-chart analysis under specific local patent rules and Federal Circuit case law is attorney work.