Based on Ethereum ethereum logo Blockchain


A decentralized autonomous organization that delivers
fast, affordable and transparent justice for all.


Smart contracts are designed to self-execute, but not to evaluate subjective information or to interpret complex evidence.

Kleros uses blockchain and crowdsourcing for evaluating complex evidence and adjudicating claims in a fast, transparent and decentralized way.

How it works?
screen mac kleros


contract kleros


Users create a smart contract and choose Kleros as adjudication protocol.

dispute kleros


The relevant information is securely sent to Kleros.

jury kleros


A tribunal is drawn from the crowd. Jurors evaluate evidence and cast their vote.

decision kleros


The decision is enforced by the smart contract.


Kleros can be used for dispute resolution and in a large number of situations where a decision has to be made transparently because it affects the interest of parties.

An entrepreneur hires a freelancer for a software development gig.
A dispute arises about the scope of the contract.

Should the freelancer give the money back to his client?

A jury of software experts analyze the evidence and votes a verdict.
A smart contract transfers the money to the winning party.

kleroterion kleros

The Kleroterion was an allotment machine used by the Athenian polis to select citizens to court juries.

On trial days, citizen wishing to serve as jurors went to the courthouse and inserted their pinakion (a bronze ID token) into a slot of the Kleroterion. A justice official threw white and black dice on a tube attached on a side of the machine. Candidates having a black ball on their row were dismissed. Candidates with a white ball were selected for paid jury duty.




An entrepreneur hires a freelancer for a software development gig. A dispute arises about the scope of the contract. A jury of software experts analyze the evidence and votes a verdict. A smart contract transfers the money to the winning party.



A startup raises money with a crowdfunding campaign. Funds will be released after the company presents a working prototype. The company presents a prototype and requests that the funds be disbursed. Kleros jurors vote that the prototype does not meet the requirements. The payment is withheld.



Federico Ast

Federico Ast

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Clément Lesaege

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Sam Vitello

Nicolas Wagner

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Want to contribute to
the justice revolution?

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Sam Vitello

Sam Vitello

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Romina Kavcic

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Maria T. Vidal

Maria T. Vidal


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Sam Vitello

Enrique Piqueras

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William George

William George


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Addison Huegel

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Ryan Polychain

Ryan Zurrer


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A decision protocol is a procedure that follows a number of steps to reach a result. Kleros is a protocol that selects, organizes, and incentivizes a tribunal of experts to make transparent decisions. The tribunal is dissolved after the decision is made.
In Ancient Athens, all citizens had the right to opt-in for paid jury duty for court and public office. In order to avoid corruption and collusion, the Greek developed a sophisticated selection procedure. Citizens were drawn by sortition (kleros) using an allotment machine called kleroterion (sortition machine). Kleros is inspired by the sortition principle used in Greek democracy. Hence, the name.
Sortition is the random selection of political officials from a pool of eligible candidates. Throughout history, political systems have used sortition in order to avoid corruption, collusion and factions. In Classical Athens, randomly selected citizens carried out most administrative duties. Florence and Venice, the most prosperous city states of the Renaissance, mixed random selection with voting. The founding fathers of the United States discussed sortition for selecting the President and decided to use it for jury selection in the justice system. Modern political theorists believe that sortition has the potential of correcting many of the flaws of representative democracy. To know more about the potential of sortition for improving governance, take a look at these books: The Principles of Representative Government, The Political Potential of Sortition: A study of the random selection of citizens for public office and Sortition: Theory and Practice.
Kleros’ early applications are connected to small claim arbitration, such as freelance software development. Over time, the protocol will be used for a wide range of decisions requiring technical expertise for the allocation of resources (real or symbolic) between parties. For example:
  • Doctors evaluating if a patient is eligible for receiving an organ for a transplant.
  • Scholars deciding if a paper should be accepted for publication.
  • Recruiters evaluating a candidate for a government position.
  • Moderators deciding if a user violated terms and conditions in a social media platform.
  • Technical experts evaluating if a song infringed copyright.
  • Analysts deciding if a user cheated in an e-gaming tournament.
Kleros relies on concepts from game theory, cryptography and blockchain for securing evidence, selecting jurors and providing incentives to make honest decisions. The protocol token (the pinakion, PNK) is used for jurors deposits. Jurors voting incoherently loose some tokens to coherent jurors. Incentives are based on a game theoretical concept known as focal point. The fundamental insight is that jurors voting coherently with the majority should be rewarded. Jurors voting incoherently should be punished. Users doing high quality and honest work will make money. Users doing poor quality or dishonest work will lose money. To learn more about the incentive structure, read our white paper.
The number of jurors is decided by the parties. They may agree to have one, three, five or any number of jurors. If, after a decision is made, one of the parties is not satisfied, it can appeal and have the decision reviewed. The case will be sent to a new tribunal with twice as many jurors.
Since decisions affect the allocation of resources, parties may try to intimidate or bribe the tribunal. Jurors are anonymous in order to protect them from intimidation and retaliation.
Satoshi Nakamoto taught us that a number of anonymous computers who do not trust each can still reach consensus, provided incentives are correctly structured. Kleros extends this principle to human decision making. A number of anonymous jurors who do not trust each other can reach consensus on a right decision, provided incentives are correctly structured. To learn more, read our white paper.
Kleros is an opt-in system, which means that parties have to accept it beforehand. Enforcement mechanisms will depend on the use case. In arbitration applications (e.g., small claims), enforcement could be made by the government as in any private arbitration court. In financial applications, funds could stay in escrow to be enforced by a smart contract when the decision is made. In other cases, Kleros decisions could be enforced by the partner. Imagine a decentralized social media platform using Kleros to punish abuse. Kleros jury will decide whether abuse existed in a specific case. Then, the social media platform enforces the decision by taking reputation points away from the abuser. In this case, the use of the platform automatically implies accepting Kleros as dispute resolution mechanism.
Anyone can earn money as a juror in the Kleros network. The better the quality of your work, the more money you can make as a juror. We are starting a number of pilots. If you would like to participate, please contact us.
Yes. We are starting to run pilots in a number of use cases. Please contact us to see if your case is eligible for a pilot.
Kleros is an emerging technology involving blockchain, game theory, collective intelligence, business, political science and law. We are actively looking for Masters and PhD students as well as senior scholars wishing to study Kleros. Scholarly contributions will help improve our technology and have a meaningful impact in the world. If you want to do research about Kleros, please contact us.
Yes, we are actively seeking technical talent. Please contact us.
Kleros is an open source project that works as a decentralized autonomous organization on Ethereum. The community is the owner of Kleros and decide the evolution of the protocol with a liquid democracy mechanism.