Rule 55.03.Signing of Pleadings, Motions and Other Papers; Representations to Court; Sanctions.
Part I · Rule 55: Pleadings, Motions and Hearing · Last amended July 1, 2025 · Last verified July 22, 2026
In one sentenceRule 55.03 requires an attorney or self-represented party to sign every filing, certifying it isn’t for an improper purpose and rests on a factual and legal basis, and lets a court impose sanctions for frivolous filings after notice and a 30-day safe harbor.
(a)Signature Required. Every pleading, motion and other filing shall be signed by at least one attorney of record in the attorney's individual name or by the self-represented party. An attorney who assists in the preparation of a pleading, motion, or other filing for an otherwise self-represented person is not required to sign the document.
Below the signature shall be printed the signer's name, Missouri bar number (if applicable), address, telephone number, facsimile number, and electronic mail address, if any.
An unsigned filing shall be stricken unless the omission is corrected promptly after being called to the attention of the attorney or party filing same.
(b)Representation to the Court. By presenting and maintaining a claim, defense, request, demand, objection, contention, or argument in a pleading, motion, or other paper filed with or submitted to the court, an attorney or party is certifying that to the best of the person's knowledge, information, and belief, formed after an inquiry reasonable under the circumstances, that:
(1)The claim, defense, request, demand, objection, contention, or argument is not presented or maintained for any improper purpose, such as to harass or to cause unnecessary delay or needless increase in the cost of litigation;
(2)The claims, defenses, and other legal contentions therein are warranted by existing law or by a nonfrivolous argument for the extension, modification, or reversal of existing law or the establishment of new law;
(3)The allegations and other factual contentions have evidentiary support or, if specifically so identified, are likely to have evidentiary support after a reasonable opportunity for further investigation or discovery. An attorney providing drafting assistance may rely on the otherwise self-represented person's representation of facts, unless the attorney knows that such representations are false; and
(4)The denials of factual contentions are warranted on the evidence or, if specifically so identified, are reasonably based on a lack of information or belief.
(c)Sanctions. If after notice and a reasonable opportunity to respond the court finds that Rule 55.03(b) has been violated, the court, subject to the conditions below, may impose an appropriate sanction upon the lawyers, law firms, or parties that have committed or are responsible for the violation.
(1)How Initiated.
(A)By Motion. A motion for sanctions under this Rule 55.03 shall be made separately from other motions or requests and shall describe the specific conduct alleged to violate Rule 55.03(b). The motion shall be served as provided in Rule 43.01. The motion shall not be filed with or presented to the court unless, within 30 days after service of the motion, the challenged claim, defense, request, demand, objection, contention, or argument is not withdrawn or appropriately corrected. If warranted, the court may award to the party prevailing on the motion the reasonable expenses and attorney's fees incurred in representing or opposing the motion. Absent exceptional circumstances a law firm shall be held jointly responsible for violations committed by its partners, associates, or employees.
(B)On Court's Initiative. On its own initiative the court may enter an order describing the specific conduct that appears to violate Rule 55.03(b) and directing a lawyer, law firm or party to withdraw or correct the questioned claim, defense, request, demand, objection, contention or argument or to show cause why it has not violated the rule with respect thereto.
(2)Nature of Sanction - Limitations. A sanction imposed for violation of this Rule 55.03 shall be limited to that which is sufficient to deter repetition of the conduct or comparable conduct by others similarly situated. Subject to the limitations in Rule 55.03(c)(1), the sanction may consist of or include directives of a nonmonetary nature, an order to pay a penalty into court, or, if imposed on motion and warranted for effective deterrence, an order directing payment to the movant of some or all of the reasonable attorney's fees and other expenses incurred as a direct result of the violation.
(A)Monetary sanctions shall not be awarded against a represented party for a violation of Rule 55.03(b)(2).
(B)Monetary sanctions shall not be awarded on the court's initiative unless the court issues its order to show cause before a voluntary dismissal or settlement of the claims made by or against the party that is, or whose lawyers are, to be sanctioned.
(3)Order. When imposing sanctions, the court shall describe the conduct determined to constitute a violation of this Rule 55.03 and explain the basis for the sanction imposed.
(d)Inapplicability to Discovery. This Rule 55.03 does not apply to disclosures and discovery requests, responses, objections, and motions that are subject to the provisions of Rules 56 to 61.
(e)Sanctions for Conduct in Prior Action. If conduct constituting a violation of Rule 55.03(b) occurs but the civil action is dismissed and if a civil action based upon or including the same claim against the same party is thereafter filed, the court, on its own motion or on motion of a party to the first action, may impose an appropriate sanction in the second action for the violation of Rule 55.03(b). The sanction shall be imposed in the manner provided by Rule 55.03(c). In determining the sanction to impose, the court shall consider the costs and expenses incurred in the action previously dismissed, including the reasonable attorney's fees incurred in the first action.
Amendment History
Adopted Jan. 19, 1973, eff. Sept. 1, 1973. Amended Nov. 21, 1985, eff. July 1, 1986; Amended June 1, 1993, eff. Jan. 1, 1994; Amended June 17, 2004, eff. Jan. 1, 2005; Amended Dec. 21, 2007, eff. July 1, 2008; Amended June 23, 2008, eff. July 1, 2008. Amended May 26, 2010, eff. July 1, 2010; Amended Dec. 27, 2012, eff. July 1, 2013; amended effective January 1, 2023; amended Sept. 3, 2024, effective July 1, 2025.
Plain-English Summary
Every pleading, motion, or other filing needs a signature — from at least one attorney of record or from the self-represented party — with the signer’s name, bar number, address, phone number, and email printed below it. An attorney who only helps draft a filing for someone who remains otherwise self-represented doesn’t have to sign. An unsigned filing gets struck unless the problem is fixed promptly once someone points it out.
By presenting or maintaining a position in a filing, the signer certifies four things after a reasonable inquiry: the position isn’t there to harass, delay, or run up costs; the legal contentions are warranted by existing law or a nonfrivolous argument for changing it; the factual contentions have evidentiary support or a reasonable prospect of getting it through further investigation or discovery; and any denials are warranted by the evidence or a reasonable lack of information. An attorney giving drafting help to an otherwise self-represented person can rely on that person’s factual representations unless the attorney knows they’re false.
Sanctions for violating this certification require notice and a chance to respond first. A sanctions motion must stand alone, describe the specific conduct at issue, and can’t be filed or presented to the court until 30 days after service — a safe harbor during which the challenged position can be withdrawn or corrected. Courts can also raise the issue on their own initiative through a show-cause order. Any sanction imposed has to be limited to what’s needed to deter repeat conduct, monetary sanctions can’t be imposed against a represented party for legal-contention violations, and monetary sanctions on the court’s own initiative are barred once a voluntary dismissal or settlement has already occurred. Law firms are generally held jointly responsible for their partners’, associates’, and employees’ violations.
The rule doesn’t reach discovery filings — those are governed separately by the discovery rules — and its reach can extend to conduct in a case that was dismissed and refiled, letting a court sanction the earlier misconduct in the second action and weigh the costs incurred in the first one.
Frequently Asked Questions
What does signing a pleading certify in Missouri?
That the filing isn’t for an improper purpose, the legal positions are warranted or nonfrivolous, and the factual contentions have or can reasonably get evidentiary support.
Can I be sanctioned for a frivolous filing in Missouri court?
Yes, under Rule 55.03(c), but only after notice and an opportunity to respond, and subject to limits on the type and size of the sanction.
What is the safe harbor period before a sanctions motion?
A sanctions motion can’t be filed until 30 days after it’s served on the other side, giving them a chance to withdraw or fix the challenged position first.
Does Rule 55.03 apply to discovery disputes?
No. The rule expressly excludes disclosures, discovery requests, responses, objections, and related motions, which fall under the separate discovery rules.
Can a law firm be sanctioned along with an individual attorney?
Generally yes — the rule holds a law firm jointly responsible for violations by its partners, associates, or employees absent exceptional circumstances.
Source & verification. Rule text and amendment history are
reproduced verbatim from the Missouri State & Federal Court Rules, adopted by the
Supreme Court of Missouri. Last verified July 22, 2026. ·
Official source
Also known as:sanctions for frivolous filingssigning pleadingsRule 11 analogcertification of pleadingssafe harbor sanctions motionattorney certification requirement