what was the shortest?
Until very recently, the Federal Rules of Procedure had a set of complaint forms that illustrated a bare minimum safe harbor that was legally sufficient to be valid.
These forms provided for a complaint of a single page with just a few lines of body text apart from the caption and signature block. In limited jurisdiction courts in collection cases, complaints of less than one page with fewer than 100 words of body text are routine.
What was the longest not stricken complaint filed in any U.S. court in
the history of the U.S.?
The longest complaint language is much harder to answer. There is no comprehensive database. So, one has to turn to appellate court rulings on complaints dismissed for being too long, and to media reports.
The governing rule in federal court is Federal Rule of Civil Procedure 8, so annotations to that rule of court decisions interpreting it are the natural place to begin to look. As a practical matter, complaints are far more often dismissed for not saying enough than for saying too much.
A rare such case said this about the Complaint before it (although it doesn't appear to have had all that many pages):
The amended complaint is still extremely verbose and rambling, and
contains a lengthy recital of evidentiary matters, examples of
which are paragraphs 26, 32, and 36. It is filled with historical and
background material which is totally irrelevant to a bill for
accounting. Much of the material therein is still scandalous and
vituperative. In short, the amended complaint may be characterized,
just as could be the original complaint, by the language of the Court
of Appeals for this Circuit in the case of McCoy, et al. v. Providence
Journal, 190 F.2d 760, 766:
‘It is hard to imagine a pleading more completely at variance with the
letter and the spirit of Rule 8(e)(1) which requires that each
averment of a pleading be ‘simple, concise and direct’.'
Martin v. Hunt, 29 F.R.D. 14, 15–16 (D. Mass. 1961).
A 317 page complaint in a securities fraud complaint that attempted to incorporate as many facts as possible, and repeated many allegations three or four times was too long and striken. In re Metropolitan Securities Litigation, 532 F.Supp.2d 1260 (E.D. Wash 2007). On the other hand a 70 page complaint with 30 pages of exhibits in a class action securities fraud case was not too long. In re Intuitive Surgical Securities Litigation, 65 F.Supp.3d 821 (N.D.Cal.2014).
Another 300+ page pro se complaint against mortgage broker and others was held to be too long when it contained over 1,000 specifically numbered paragraphs and hundreds of additional, non-numbered paragraphs, was disjointed and unorganized as whole, and contained hundreds of paragraphs that were irrelevant or were relevant only to claims that had already been dismissed with prejudice. Grimes v. Fremont General Corp., 933 F.Supp.2d 584 (S.D.N.Y.2013).
In general, complaints are held to be too long when they are not only long in absolute terms, but also contain repetition, irrelevant material, or don't have almost every paragraph advance the general narrative.
For example, a pro se plaintiff's 56-page complaint alleging negligence was too long where it consisted of poorly numbered paragraphs that combined different sets of circumstances in disorganized fashion. Cintron-Luna v. Roman-Bultron, 668 F.Supp.2d 315 (D.Puerto Rico 2009). Typically, a simple negligence complaint would be only five to fifteen pages long with no exhibits.
Similarly, a complaint of 96 pages, much of which consisted of background information, was held to be too long, although the remedy was for the court to strike irrelevant or unnecessary parts of the complaint, effectively editing it, rather than dismissing the complaint in its entirety, and demanding that the plaintiff start over. Verfuerth v. Orion Energy Systems, Inc., 65 F.Supp.3d 640 (E.D.Wis.2014).
On the other hand, it wouldn't be unusual for a law firm to file a commercial debt collection case, perhaps foreclosing on a mortgage of business real estate in a shopping center or high rise, or in an HOA dispute, to have a complaint of ten or twenty pages supported by all of the core contractual documents of the mortgage or homeowner's association as exhibits, that would run to 50-100 pages.
Standards for complaint length have evolved over time. In 1946, a 14 page complaint with 17 pages of exhibits was stricken for being too long. Renshaw v. Renshaw, 153 F.2d 310 (D.C. App. 1946).
I've personally seen complaints of about 120 pages in the early 1990s in relatively straightforward civil rights cases stricken for being too long, but complaints of 20-40 pages with additional exhibits running dozens of more pages aren't uncommon in a complex fact pattern.
Historical context does matter. There were four phases of pleading at the federal level, most of which were also present at the state level. And, in general, courts have become more tolerant of long complaints with many long exhibits in recent times.
The first was "common law pleading" which was quite arcane with a lot of idiosyncratic rules. For some kinds of claims this produced very short complaints, for other kinds of claims this demanded very long complaints.
The second was pleading based upon New York States's Field Code, which required the pleading of non-conclusory facts in support of each element of the claim asserted in the case, but that legal authority should generally not be referenced unless a specific statute was at issue. This standard produced complaints similar in length to the current standard, but usually somewhat shorter in practice.
The third was pleading based upon the federal rules of civil procedure as reformed in the 1930s, which required a "short and plain" statement of the facts merely sufficient to put the defendant on notice of the nucleus of facts giving rise to the dispute with the safe harbor federal rules of civil procedure as a guide. Under this standard a case could be dismissed on the face of the complaint only if no relief would be available on any set of facts consistent with the allegations of the complaint, even if it seemed far fetched and did not set forth facts in support of every element of a claim. This was the most bare bones stage of federal pleading and is still the de jure standard in some state and local courts, and the de facto standard in most courts of limited jurisdiction (e.g. hearing claims only up to $15,000).
The fourth and current standard of plausibility pleading, in which non-conclusory specific facts must be set forth sufficient to support the material elements of a claim for relief in a manner that is plausible in the eyes of the judge under a pair of U.S. Supreme Court cases known as Twombly and Iqbal. The fact that relief would be possible consistent with the facts set forth in the complaint, if it is not enough to make success plausible, is insufficient. Also, under this standard, one must have actual knowledge of the facts in support of a claim, rather than making allegations of facts necessary to make a claim plausible based merely upon "information and belief." This makes complaints significantly longer. Given the vast discretion inherent in determining if a complaint is "plausible" in some areas of the law, there is a strong incentive to "over write" a complaint so that it includes detail that may not be legally necessary, because you don't know in advance how picky or skeptical the judge that your case is assigned to will be.
In addition to these four legal standards, the other issue is technology. It is much easier to cut and paste language into a complaint, and to attach copies of key documents supporting a legal case, than it was prior to computers and photocopiers and scanners and printers. The advent of electronic filing made filing of a long complaint even easier, avoiding the need to mail or hand deliver a large stack of documents in many cases.
From a comparative perspective, there was once a time in recent history in Spanish jurisprudence, when, to file a lawsuit, you needed to include all of the documentary evidence and affidavits you intended to present in the case, literally wrapped in a ribbon. Complaints in that judicial regime, were, of course, much, much longer than in other court systems.