Smart Contracts - Kleros Documentation

Core Data Structures

Item Struct

struct Item {
    Status status;                         // Current state
    uint256 sumDeposit;                    // Total locked deposits
    uint256 requestCount;                  // Number of requests
    mapping(uint256 => Request) requests;  // Request history
}

Request Struct

struct Request {
    RequestType requestType;         // Registration or Clearing
    uint64 submissionTime;           // When submitted
    uint24 arbitrationParamsIndex;   // Preserves original arbitrator settings
    address payable requester;       // Who submitted
    address payable challenger;      // Who challenged (if any)
}

Arbitration Parameters

struct ArbitrationParams {
    IArbitratorV2 arbitrator;        // Kleros Court contract
    bytes arbitratorExtraData;       // Court ID + juror count
    EvidenceModule evidenceModule;   // Evidence storage contract
}

Enumerations

enum Status {
    Absent,                // Item does not exist
    Registered,            // Item is active in registry
    RegistrationRequested, // Pending addition
    ClearingRequested      // Pending removal
}

enum RequestType {
    Registration,  // Adding item
    Clearing       // Removing item
}

Initialization

Initialize Function

function initialize(
    address _governor,                       // Admin address
    IArbitratorV2 _arbitrator,              // Kleros Core
    bytes calldata _arbitratorExtraData,    // Court config
    EvidenceModule _evidenceModule,          // Evidence storage
    address _connectedList,                  // Optional parent list
    TemplateRegistryParams calldata _templateRegistryParams,
    uint256[4] calldata _baseDeposits,       // Deposit amounts
    uint256 _challengePeriodDuration,        // Challenge window
    address _relayerContract,                // Direct operations
    string calldata _listMetadata            // JSON string
) external

Base Deposits Array

Index	Purpose
0	Submission base deposit
1	Removal base deposit
2	Submission challenge deposit
3	Removal challenge deposit

Example Initialization

// Court ID must be uint96, juror count uint256 — matches IArbitratorV2 spec
const extraData = ethers.solidityPacked(
  ["uint96", "uint256"],
  [1, 3] // Court ID 1 (General Court), 3 jurors
);

await curate.initialize(
  governorAddress,
  klerosCore.target,
  extraData,
  evidenceModule.target,
  ethers.ZeroAddress,           // No connected list
  {
    templateRegistry: templateRegistry.target,
    registrationTemplateParameters: [template, mappings],
    removalTemplateParameters: [template, mappings]
  },
  [
    ethers.parseEther("0.001"), // submission
    ethers.parseEther("0.001"), // removal
    ethers.parseEther("0.001"), // submission challenge
    ethers.parseEther("0.001")  // removal challenge
  ],
  3600,                         // 1 hour challenge period
  relayerAddress,
  JSON.stringify(metadata)
);

Challenge Period Guidelines:

Testnet: 3600 seconds (1 hour)
Mainnet: 259200-604800 seconds (3-7 days)

Item Data Format

Items in Curate V2 are stored as a JSON string. The registry’s listMetadata defines the schema via a columns array, and each item matches those columns:

{
  "columns": [
    { "label": "Name",        "description": "Token name",            "type": "text",    "isIdentifier": true },
    { "label": "Address",     "description": "Contract address",      "type": "address", "isIdentifier": true },
    { "label": "Symbol",      "description": "Token ticker symbol",   "type": "text" },
    { "label": "Decimals",    "description": "Number of decimals",    "type": "number" },
    { "label": "Logo",        "description": "IPFS URI of token logo","type": "image" }
  ]
}

A submitted item must be a JSON object with one key per column label:

{
  "Name": "Dai Stablecoin",
  "Address": "0x6B175474E89094C44Da98b954EedeAC495271d0F",
  "Symbol": "DAI",
  "Decimals": 18,
  "Logo": "/ipfs/QmDAI..."
}

The itemID is keccak256(abi.encodePacked(itemJSON)) — the hash of the exact JSON string submitted. The data mappings system uses this column structure to extract {{itemName}} and {{itemDescription}} template variables.

`arbitrationParamsIndex` — Versioning

Each Request stores a uint24 arbitrationParamsIndex that snapshots the registry’s arbitration parameters at submission time. This is critical: if the governor updates the arbitrator or extraData after a request is submitted, the original parameters are preserved for that request’s challenge and dispute lifecycle. This means:

Challengers must use the same arbitrationParamsIndex as the original submission — fetch it from the request before challenging
Cost calculations must use the arbitration params at request.arbitrationParamsIndex, not the current params

// Get the arbitration params for a specific request
(uint256 reqCount,) = curate.getItemInfo(itemId);
(,, uint24 paramsIndex,,) = curate.getRequestInfo(itemId, reqCount - 1);
(IArbitratorV2 arb, bytes memory extraData,) = curate.arbitrationParamsAt(paramsIndex);
uint256 cost = arb.arbitrationCost(extraData);

Registration vs Removal — Separate Dispute Templates

Curate V2 uses two separate dispute templates: one for registration requests and one for removal (clearing) requests. They have different answer logic:

Template	Question	Answer 0x01	Answer 0x02
Registration	”Does item comply with criteria?”	Yes, Add Item	No, Reject Item
Removal	”Should item be removed?”	Yes, Remove Item	No, Keep Item

Both are set at initialization via TemplateRegistryParams.registrationTemplateParameters and removalTemplateParameters. You must provide both, and they must be consistent with your policy document.

Item Submission

Add Item

function addItem(string calldata _item) external payable returns (bytes32 itemID)

Parameters:

_item: JSON string matching the registry’s column schema (see Item Data Format above)

Returns:

itemID: keccak256 hash of the item string

Calculate Submission Cost

// Get required deposit
const deposit = await curate.submissionBaseDeposit();

// Get arbitration cost
const arbitrator = await curate.getArbitrator();
const extraData = await curate.getArbitratorExtraData();
const arbCost = await arbitrator.arbitrationCost(extraData);

// Total required
const totalCost = deposit + arbCost;

Submission Example

const itemData = {
  address: "0x1234...",
  name: "Token Name",
  symbol: "TKN"
};
const itemString = JSON.stringify(itemData);

// Calculate item ID
const itemID = ethers.keccak256(ethers.toUtf8Bytes(itemString));

// Submit item
const tx = await curate.addItem(itemString, { value: totalCost });
await tx.wait();

console.log("Item ID:", itemID);

Item Removal

Remove Item

function removeItem(bytes32 _itemID, string calldata _evidence) external payable

Parameters:

_itemID: Hash of the item to remove
_evidence: JSON evidence string supporting removal

Removal Example

const evidence = JSON.stringify({
  name: "Removal Request",
  description: "This item violates the policy because...",
});

const deposit = await curate.removalBaseDeposit();
const arbCost = await arbitrator.arbitrationCost(extraData);
const totalCost = deposit + arbCost;

const tx = await curate.removeItem(itemID, evidence, { value: totalCost });
await tx.wait();

Challenging Requests

Challenge Request

function challengeRequest(bytes32 _itemID, string calldata _evidence) external payable

Parameters:

_itemID: Item with pending request
_evidence: JSON evidence supporting challenge

Challenge Example

// Determine challenge deposit based on request type
const [status] = await curate.getItemInfo(itemID);
const challengeDeposit = status === 2 // RegistrationRequested
  ? await curate.submissionChallengeBaseDeposit()
  : await curate.removalChallengeBaseDeposit();

const arbCost = await arbitrator.arbitrationCost(extraData);
const totalCost = challengeDeposit + arbCost;

// Prepare evidence
const evidence = JSON.stringify({
  name: "Invalid Submission",
  description: "This item violates the list policy because...",
  supportingInfo: "Reference: [link or details]"
});

// Submit challenge
const tx = await curate.challengeRequest(itemID, evidence, {
  value: totalCost
});
await tx.wait();

Challenges must be submitted during the challenge period. Check timing before challenging.

Executing Requests

Execute Request

function executeRequest(bytes32 _itemID) external

Executes an unchallenged request after the challenge period has passed.

Execution Example

// Check if challenge period has passed
const [status, requestCount] = await curate.getItemInfo(itemID);
const lastRequestIndex = requestCount - 1;

const requestInfo = await curate.getRequestInfo(itemID, lastRequestIndex);
const challengePeriod = await curate.challengePeriodDuration();
const now = Math.floor(Date.now() / 1000);

if (now > requestInfo.submissionTime + challengePeriod) {
  const tx = await curate.executeRequest(itemID);
  await tx.wait();
  console.log("Request executed - deposit refunded");
}

Query Functions

Get Item Info

function getItemInfo(bytes32 _itemID) external view returns (
    Status status,
    uint256 requestCount
)

Get Request Info

function getRequestInfo(bytes32 _itemID, uint256 _requestID) external view returns (
    RequestType requestType,
    uint64 submissionTime,
    bool disputed,
    bool resolved,
    address requester,
    address challenger
)

View Contract Functions

The CurateView contract provides enhanced batch queries:

// Get complete registry configuration
function fetchArbitrable(address _curate) external view returns (
    address governor,
    address relayerContract,
    uint256 submissionBaseDeposit,
    uint256 removalBaseDeposit,
    uint256 submissionChallengeBaseDeposit,
    uint256 removalChallengeBaseDeposit,
    uint256 challengePeriodDuration,
    uint256 arbitrationCost
)

// Get item with latest request
function getItem(address _curate, bytes32 _itemID) external view returns (
    Status status,
    bool disputed,
    uint256 sumDeposit,
    address requester
)

// Get all requests for an item
function getItemRequests(address _curate, bytes32 _itemID) external view returns (
    Request[] memory
)

View Contract Example

const view = await ethers.getContractAt("CurateView", VIEW_ADDRESS);

// Get complete registry configuration
const config = await view.fetchArbitrable(curateAddress);
console.log("Challenge period:", config.challengePeriodDuration.toString());
console.log("Submission deposit:", ethers.formatEther(config.submissionBaseDeposit));

// Get item details
const item = await view.getItem(curateAddress, itemID);
console.log("Status:", ["Absent", "Registered", "RegRequested", "ClearRequested"][item.status]);
console.log("Disputed:", item.disputed);

// Get all requests
const requests = await view.getItemRequests(curateAddress, itemID);
requests.forEach((req, i) => {
  console.log(`Request ${i}:`, {
    disputed: req.disputed,
    resolved: req.resolved,
    requester: req.requester
  });
});

Governor Functions

Configuration Updates

// Change arbitrator settings
function changeArbitrator(
    IArbitratorV2 _arbitrator,
    bytes calldata _arbitratorExtraData
) external onlyGovernor

// Update base deposits
function changeBaseDeposits(uint256[4] calldata _baseDeposits) external onlyGovernor

// Modify challenge period
function changeChallengePeriodDuration(uint256 _challengePeriodDuration) external onlyGovernor

// Set connected list (for hierarchical registries)
function changeConnectedList(address _connectedList) external onlyGovernor

// Update list metadata
function changeListMetadata(string calldata _listMetadata) external onlyGovernor

// Change relayer contract
function changeRelayerContract(address _relayerContract) external onlyGovernor

Direct Item Management

// Add item bypassing challenge period (governor/relayer only)
function addItemDirectly(string calldata _item) external onlyGovernorOrRelayer

// Remove item bypassing challenge period (governor/relayer only)  
function removeItemDirectly(bytes32 _itemID) external onlyGovernorOrRelayer

Events

Item Lifecycle Events

// New item submitted
event NewItem(
    bytes32 indexed itemID,
    string data,
    bool addedDirectly
);

// Item status changed
event ItemStatusChange(
    bytes32 indexed itemID,
    bool updatedDirectly
);

// Request submitted
event RequestSubmitted(
    bytes32 indexed itemID,
    uint256 requestID
);

Dispute Events

// Dispute created in Kleros Court
event DisputeRequest(
    IArbitratorV2 indexed arbitrator,
    uint256 indexed disputeID,
    uint256 externalDisputeID,
    uint256 templateId,
    string templateUri
);

// Ruling received from arbitrator
event Ruling(
    IArbitratorV2 indexed arbitrator,
    uint256 indexed disputeID,
    uint256 ruling
);

Configuration Events

// Connected list updated
event ConnectedListSet(address indexed connectedList);

// Metadata updated
event ListMetadataSet(string listMetadata);

Access Control

Governor Modifier

modifier onlyGovernor() {
    require(msg.sender == governor, "Must be governor");
    _;
}

Relayer Modifier

modifier onlyRelayer() {
    require(msg.sender == relayerContract, "Must be relayer");
    _;
}

Combined Access

modifier onlyGovernorOrRelayer() {
    require(
        msg.sender == governor || msg.sender == relayerContract,
        "Must be governor or relayer"
    );
    _;
}

Security Considerations

Reentrancy Protection

Uses .send() with 2300 gas limit for refunds
State updates occur before external calls
No direct .call() usage for ETH transfers

Integer Overflow

Solidity 0.8.24 has built-in overflow protection
uint24 arbitrationParamsIndex allows 16,777,215 changes

Timestamp Manipulation

Challenge periods use block.timestamp
Can be manipulated ±15 seconds by miners
Use sufficiently long periods (hours/days minimum)

Best Practices

// Always validate item doesn't exist before submission
const [status] = await curate.getItemInfo(itemID);
if (status !== 0) {
  throw new Error("Item already exists");
}

// Check challenge period before challenging
const [, requestCount] = await curate.getItemInfo(itemID);
const request = await curate.getRequestInfo(itemID, requestCount - 1);
const challengePeriod = await curate.challengePeriodDuration();
const now = Math.floor(Date.now() / 1000);

if (now > request.submissionTime + challengePeriod) {
  throw new Error("Challenge period expired");
}

// Handle transaction errors
try {
  const tx = await curate.addItem(itemData, { value: totalCost });
  await tx.wait();
} catch (error) {
  if (error.code === 'INSUFFICIENT_FUNDS') {
    console.error("Not enough ETH");
  } else if (error.message.includes("Item must be absent")) {
    console.error("Item already exists");
  }
  throw error;
}

Getting Started

Building Arbitrable Apps (V2)

Building on Kleros Products

Cross-chain

Examples

Subgraph & Data

V1 Integration (Legacy)

Documentation Index

​Core Data Structures

​Item Struct

​Request Struct

​Arbitration Parameters

​Enumerations

​Initialization

​Initialize Function

​Base Deposits Array

​Example Initialization

​Item Data Format

​arbitrationParamsIndex — Versioning

​Registration vs Removal — Separate Dispute Templates

​Item Submission

​Add Item

​Calculate Submission Cost

​Submission Example

​Item Removal

​Remove Item

​Removal Example

​Challenging Requests

​Challenge Request

​Challenge Example

​Executing Requests

​Execute Request

​Execution Example

​Query Functions

​Get Item Info

​Get Request Info

​View Contract Functions

​View Contract Example

​Governor Functions

​Configuration Updates

​Direct Item Management

​Events

​Item Lifecycle Events

​Dispute Events

​Configuration Events

​Access Control

​Governor Modifier

​Relayer Modifier

​Combined Access

​Security Considerations

​Best Practices

Core Data Structures

Item Struct

Request Struct

Arbitration Parameters

Enumerations

Initialization

Initialize Function

Base Deposits Array

Example Initialization

Item Data Format

`arbitrationParamsIndex` — Versioning

Registration vs Removal — Separate Dispute Templates

Item Submission

Add Item

Calculate Submission Cost

Submission Example

Item Removal

Remove Item

Removal Example

Challenging Requests

Challenge Request

Challenge Example

Executing Requests

Execute Request

Execution Example

Query Functions

Get Item Info

Get Request Info

View Contract Functions

View Contract Example

Governor Functions

Configuration Updates

Direct Item Management

Events

Item Lifecycle Events

Dispute Events

Configuration Events

Access Control

Governor Modifier

Relayer Modifier

Combined Access

Security Considerations

Best Practices