River Markets

River Markets is a unified prime brokerage for prediction markets, consolidating multiple exchanges — Kalshi, Polymarket, and Polymarket US (with Novig and Rothera planned) — behind a single account, order-management system, and REST + WebSocket API. Every contract across all venues is assigned a unified River ID, so professional and institutional traders can search markets, place and route orders (including icebergs, pegs, stop-losses, and take-profits with smart order routing), track positions and P&L across isolated subaccounts, and stream live fills, orderbooks, orders, and trade prints from one integration. Requests are Ed25519-signed so the private key never leaves the client process. Founded by ex-BlackRock and high-frequency trading quants and backed by Y Combinator (Spring 2026).

River Markets publishes 13 APIs on the APIs.io network, including balance API, complex-orders API, fair-values API, and 10 more. Tagged areas include Company, Prediction Markets, Trading, Prime Brokerage, and Financial-Services.

The River Markets catalog on APIs.io includes 1 event-driven AsyncAPI specification.

River Markets’ developer surface includes documentation, API reference, getting-started guide, signup flow, authentication, and 17 more developer resources.

🌐 Visit website 📡 Source on GitHub

39.3/100 developing ▬ flat Agent 37/100 agent ready Full breakdown ↓
scored 2026-08-20 · rubric v0.12.0

AccessSelf serve

13 APIs 1 MCP Servers

CompanyPrediction MarketsTradingPrime BrokerageFinancial-ServicesOrder ManagementMarket DataWebSocketFintech

Kin Score

Kin Score How this is scored →
scored 2026-08-20 · rubric v0.12.0

Composite quality — 39.3/100 · developing

Contract Quality 15.3 / 21

Developer Ergonomics 10.0 / 17

Access Clarity 0.0 / 17

Operational Transparency 0.3 / 11

Contract Governance 1.7 / 10

Discoverability 6.9 / 9

Regulatory Posture 4.2 / 15

Agent readiness — 37/100 · agent ready

Machine-Readable Contract 18 / 18

Agentic Access Contract 10 / 10

Documented Reversibility 6 / 6

MCP Server 0 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 8 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 6 / 6

Agent Skills 5 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Regulatory Posture applies to this provider. Its tags matched the Securities & Market Data regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/river-markets: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

APIs 13

Individual APIs this provider publishes, each with its own machine-readable definition.

Open Collections 14

Open, tool-agnostic API collections (OpenAPI-derived and Bruno).

MCP Servers 1

Model Context Protocol servers that expose these APIs to AI agents.

Get Started 3

Portal, sign-up, and the first successful call

DeveloperPortal

DeveloperPortal

GettingStarted

GettingStarted

SignUp

SignUp

Documentation 4

Reference material describing how the API behaves

Documentation

APIReference

OpenAPI

AsyncAPI

Agent Surfaces 4

MCP servers, agent skills, and machine-readable catalogs

LLMsTxt

MCPServer

AgenticAccess

AgentSkill

Design & Contract 5

Pagination, idempotency, versioning, errors, and events

Conventions

ErrorCatalog

Lifecycle

Conformance

DataModel

Build 3

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

GitHubOrganization

Packages

Packages

SDKs

SDKs

Access & Security 2

Authentication, authorization, and security posture

Authentication

Authentication

DomainSecurity

DomainSecurity

Other 1

Properties that don't map to a standard resource type

Overlay

Overlay

Source (apis.yml)

aid: river-markets
name: River Markets
description: River Markets is a unified prime brokerage for prediction markets, consolidating multiple exchanges — Kalshi,
  Polymarket, and Polymarket US (with Novig and Rothera planned) — behind a single account, order-management system, and REST
  + WebSocket API. Every contract across all venues is assigned a unified River ID, so professional and institutional traders
  can search markets, place and route orders (including icebergs, pegs, stop-losses, and take-profits with smart order routing),
  track positions and P&L across isolated subaccounts, and stream live fills, orderbooks, orders, and trade prints from one
  integration. Requests are Ed25519-signed so the private key never leaves the client process. Founded by ex-BlackRock and
  high-frequency trading quants and backed by Y Combinator (Spring 2026).
url: https://raw.githubusercontent.com/api-evangelist/river-markets/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- y-combinator
x-tier: stub
x-tier-reason: portfolio-lead
accessModel:
  pricing: unknown
  onboarding: self-serve
  trial: false
  try_now: false
  public: false
  label: Self-serve signup
  confidence: medium
  source:
  - authentication
  generated: '2026-07-22'
  method: derived
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-07-21'
x-enrichment:
  date: '2026-07-21'
  status: enriched
  artifacts_added: 17
  pass: local-v1
image: https://rivermarkets.com/favicon.ico
tags:
- Company
- Prediction Markets
- Trading
- Prime Brokerage
- Financial-Services
- Order Management
- Market Data
- WebSocket
- Fintech
tags_raw:
- Company
- Prediction Markets
- Trading
- Prime Brokerage
- Financial Services
- Order Management
- Market Data
- WebSocket
- Fintech
apis:
- aid: river-markets:river-markets-balance-api
  name: River Markets balance API
  description: The balance API from River Markets — 1 operation(s) for balance.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Balances
  tags_raw:
  - balance
  properties:
  - type: OpenAPI
    url: openapi/river-markets-balance-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-complex-orders-api
  name: River Markets complex-orders API
  description: 'Manage complex orders: conditional orders (take-profit and stop-loss), TWAP, and other advanced order types.'
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - complex-orders
  properties:
  - type: OpenAPI
    url: openapi/river-markets-complex-orders-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-fair-values-api
  name: River Markets fair-values API
  description: The fair-values API from River Markets — 2 operation(s) for fair-values.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - fair-values
  properties:
  - type: OpenAPI
    url: openapi/river-markets-fair-values-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-fills-api
  name: River Markets fills API
  description: Retrieve trade execution history and fill details.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Fills
  tags_raw:
  - fills
  properties:
  - type: OpenAPI
    url: openapi/river-markets-fills-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-generic-assets-api
  name: River Markets generic-assets API
  description: The generic-assets API from River Markets — 3 operation(s) for generic-assets.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - generic-assets
  properties:
  - type: OpenAPI
    url: openapi/river-markets-generic-assets-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-markets-api
  name: River Markets markets API
  description: Search and discover prediction markets across Kalshi and Polymarket.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Markets
  tags_raw:
  - markets
  properties:
  - type: OpenAPI
    url: openapi/river-markets-markets-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-orderbooks-api
  name: River Markets orderbooks API
  description: The orderbooks API from River Markets — 2 operation(s) for orderbooks.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Order Books
  tags_raw:
  - orderbooks
  properties:
  - type: OpenAPI
    url: openapi/river-markets-orderbooks-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-orders-api
  name: River Markets orders API
  description: Place and manage orders on prediction market exchanges.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Order
  tags_raw:
  - orders
  properties:
  - type: OpenAPI
    url: openapi/river-markets-orders-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-positions-api
  name: River Markets positions API
  description: View current portfolio positions across all connected exchanges.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Positions
  tags_raw:
  - positions
  properties:
  - type: OpenAPI
    url: openapi/river-markets-positions-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-prices-api
  name: River Markets prices API
  description: Get historical price data and candlesticks from exchanges.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Prices
  tags_raw:
  - prices
  properties:
  - type: OpenAPI
    url: openapi/river-markets-prices-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-subaccounts-api
  name: River Markets subaccounts API
  description: Manage trading subaccounts. Each subaccount can have its own exchange credentials and positions.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Subaccounts
  tags_raw:
  - subaccounts
  properties:
  - type: OpenAPI
    url: openapi/river-markets-subaccounts-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-tradeprints-api
  name: River Markets tradeprints API
  description: Recent trades for a market. Pairs with the /v1/ws/tradeprints WebSocket for live updates.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - tradeprints
  properties:
  - type: OpenAPI
    url: openapi/river-markets-tradeprints-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
- aid: river-markets:river-markets-watchlists-api
  name: River Markets watchlists API
  description: The watchlists API from River Markets — 4 operation(s) for watchlists.
  humanURL: https://docs.rivermarkets.com
  baseURL: https://api.rivermarkets.com
  tags:
  - Watchlist
  tags_raw:
  - watchlists
  properties:
  - type: OpenAPI
    url: openapi/river-markets-watchlists-api-openapi.yml
  - type: Documentation
    url: https://docs.rivermarkets.com
  - type: APIReference
    url: https://docs.rivermarkets.com/api-reference/overview
  - type: GettingStarted
    url: https://docs.rivermarkets.com/quickstart
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: DeveloperPortal
  url: https://docs.rivermarkets.com
- type: Documentation
  url: https://docs.rivermarkets.com
- type: APIReference
  url: https://docs.rivermarkets.com/api-reference/overview
- type: GettingStarted
  url: https://docs.rivermarkets.com/quickstart
- type: SignUp
  url: https://app.rivermarkets.com
- type: GitHubOrganization
  url: https://github.com/rivermarkets
- type: OpenAPI
  url: openapi/_original/river-markets-openapi-original.json
- type: Authentication
  url: authentication/river-markets-authentication.yml
- type: DomainSecurity
  url: security/river-markets-domain-security.yml
- type: LLMsTxt
  url: llms/river-markets-llms.txt
- type: Packages
  url: packages/river-markets-packages.yml
- type: SDKs
  url: packages/river-markets-packages.yml
- type: Conventions
  url: conventions/river-markets-conventions.yml
- type: ErrorCatalog
  url: errors/river-markets-problem-types.yml
- type: Lifecycle
  url: lifecycle/river-markets-lifecycle.yml
- type: Conformance
  url: conformance/river-markets-conformance.yml
- type: DataModel
  url: data-model/river-markets-data-model.yml
- type: MCPServer
  url: mcp/river-markets-mcp.yml
- type: Overlay
  url: overlays/river-markets-openapi-overlay.yaml
- type: AgenticAccess
  url: agentic-access/river-markets-agentic-access.yml
- type: AsyncAPI
  url: asyncapi/river-markets-streaming-asyncapi.yml
- type: AgentSkill
  url: skills/_index.yml