Create a market

To create a market, call one of the four creation functions on the MarketFactory contract. Each function corresponds to a market type; you pass a single CreateMarketParams struct. On success, the function returns the new market contract address (you can also read it from the NewMarket event).

Which function to use

Function	When to use it	Main parameter rules
`createCategoricalMarket`	Single-choice question (e.g. “Who will win?” → one of A, B, C).	`outcomes`: ≥ 2 labels. No bounds.
`createMultiCategoricalMarket`	Multi-choice question (e.g. “Which teams qualify?” → any subset).	`outcomes`: ≥ 2 labels. No bounds.
`createScalarMarket`	Numeric outcome in a range (e.g. “Temperature in °C?” between 0 and 50).	`outcomes`: exactly 2 (e.g. “Lower”, “Higher”). Required: `lowerBound`, `upperBound` in wei (1e18).
`createMultiScalarMarket`	Several numeric questions (e.g. one per city).	`outcomes`: ≥ 2 (e.g. city names). Use `questionStart`, `questionEnd`, `outcomeType` to build each question; market name is built from these. No bounds.

Parameters: `CreateMarketParams`

All four functions take one argument: a struct with the following fields. Optional/conditional fields are noted.

Parameter	Type	Required / notes
`marketName`	string	Yes (except multi scalar: there it is built from questionStart/outcomeType/questionEnd).
`outcomes`	string[]	Yes. Categorical/multi categorical: ≥ 2. Scalar: exactly 2. Multi scalar: ≥ 2.
`questionStart`	string	Multi scalar only: prefix for each per-outcome question.
`questionEnd`	string	Multi scalar only: suffix for each per-outcome question.
`outcomeType`	string	Multi scalar only: placeholder in market name (e.g. “City”).
`parentMarket`	address	Optional. Set for conditional markets; use `0x0` for root markets.
`parentOutcome`	uint256	Optional. For conditional markets: index of the parent outcome this market depends on.
`category`	string	Yes. Reality.eth category (e.g. “politics”, “weather”).
`lang`	string	Yes. Language code (e.g. “en_US”).
`lowerBound`	uint256	Scalar only. Minimum value in wei (use e.g. `parseEther("0")`).
`upperBound`	uint256	Scalar only. Maximum value in wei (e.g. `parseEther("50")`). Must be > lowerBound.
`minBond`	uint256	Yes. Minimum bond for answering on Reality.eth (in wei).
`openingTime`	uint32	Yes. Unix timestamp when the question becomes answerable.
`tokenNames`	string[]	Yes. ERC20 symbol for each outcome (≤31 chars), one per entry in `outcomes`.

Getting the new market address: the contract returns it; you can also parse the NewMarket event from the transaction logs. Struct shape (for ABI / viem):

struct CreateMarketParams {
    string marketName;   // Used in categorical, multi categorical, scalar. In multi scalar: built from questionStart + outcomeType + questionEnd.
    string[] outcomes;   // Market outcomes (excludes INVALID_RESULT)
    string questionStart;   // For multi scalar: prefix of each Reality question
    string questionEnd;     // For multi scalar: suffix of each Reality question
    string outcomeType;    // For multi scalar: placeholder in market name, e.g. "City"
    uint256 parentOutcome; // Optional: conditional outcome index
    address parentMarket;  // Optional: parent conditional market
    string category;       // Reality question category
    string lang;           // Reality question language
    uint256 lowerBound;    // Only for scalar: minimum value (in wei, 1e18 units)
    uint256 upperBound;    // Only for scalar: maximum value (in wei, 1e18 units)
    uint256 minBond;       // Reality min bond
    uint32 openingTime;    // Reality question opening time
    string[] tokenNames;   // ERC20 name for each outcome (≤31 chars; SER-INVALID is automatic)
}

Using @seer-pm/sdk (recommended)

The @seer-pm/sdk provides getCreateMarketParams, getCreateMarketExecution, and MarketTypes. Use your viem clients to send the transaction. See Viem setup for installation.

SDK: create categorical market

Only required: marketType, marketName, outcomes, openingTime, minBond, chainId. Other fields have defaults (e.g. tokenNames are derived from outcomes, category defaults to "misc").

import { getPublicClient, getWalletClient } from "./viem-setup";
import { gnosis } from "viem/chains";
import { getCreateMarketExecution, getNewMarketFromLogs, MarketTypes } from "@seer-pm/sdk";

const chain = gnosis;
const publicClient = getPublicClient(chain);
const walletClient = getWalletClient(chain, process.env.PRIVATE_KEY! as `0x${string}`);
const chainId = chain.id;

const execution = getCreateMarketExecution({
  marketType: MarketTypes.CATEGORICAL,
  marketName: "Who will win the election?",
  outcomes: ["Alice", "Bob", "Carol"],
  openingTime: Math.floor(Date.now() / 1000),
  minBond: 10000000000000000n,
  chainId,
  category: "politics", // optional; default "misc"
});

const hash = await walletClient.sendTransaction(execution);
const receipt = await publicClient.waitForTransactionReceipt({ hash });

const newMarketAddress = getNewMarketFromLogs(receipt.logs);
if (!newMarketAddress) throw new Error("NewMarket event not found in receipt");

SDK: create multi categorical market

const execution = getCreateMarketExecution({
  marketType: MarketTypes.MULTI_CATEGORICAL,
  marketName: "Which teams will qualify? (select all that apply)",
  outcomes: ["Team A", "Team B", "Team C"],
  openingTime: Math.floor(Date.now() / 1000),
  minBond: 10000000000000000n,
  chainId,
  category: "sports",
});

const hash = await walletClient.sendTransaction(execution);

SDK: create scalar market

For scalar, lowerBound, upperBound and unit are also required. Bounds are in wei (1e18); use viem’s parseEther (e.g. 0 and 50 for a 0–50 °C range):

import { parseEther } from "viem";
import { getCreateMarketExecution, MarketTypes } from "@seer-pm/sdk";

const execution = getCreateMarketExecution({
  marketType: MarketTypes.SCALAR,
  marketName: "What will be the temperature in °C on 2025-03-01?",
  outcomes: ["Lower", "Higher"],
  lowerBound: parseEther("0"),
  upperBound: parseEther("50"),
  unit: "°C",
  openingTime: Math.floor(Date.now() / 1000),
  minBond: 10000000000000000n,
  chainId,
  category: "weather",
});

const hash = await walletClient.sendTransaction(execution);

SDK: create multi scalar market

For multi scalar, the name must include the [outcomeType] placeholder (e.g. [City]) so the SDK can build questionStart / questionEnd / outcomeType via getQuestionParts. unit is required for the question suffix.

const execution = getCreateMarketExecution({
  marketType: MarketTypes.MULTI_SCALAR,
  marketName: "What will be the max temperature in °C on 2025-03-01 in [City]?",
  outcomes: ["Berlin", "Madrid", "Paris"],
  unit: "°C",
  openingTime: Math.floor(Date.now() / 1000),
  minBond: 10000000000000000n,
  chainId,
  category: "weather",
});

You can use getCreateMarketParams(props) if you only need the params struct (with all fields filled) for a custom flow.

Getting started

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Contracts

Create a market

Which function to use

Parameters: `CreateMarketParams`

Using @seer-pm/sdk (recommended)

SDK: create categorical market

SDK: create multi categorical market

SDK: create scalar market

SDK: create multi scalar market

​Which function to use

​Parameters: CreateMarketParams

​Using @seer-pm/sdk (recommended)

​SDK: create categorical market

​SDK: create multi categorical market

​SDK: create scalar market

​SDK: create multi scalar market

Which function to use

Parameters: `CreateMarketParams`

Using @seer-pm/sdk (recommended)

SDK: create categorical market

SDK: create multi categorical market

SDK: create scalar market

SDK: create multi scalar market