# Bellwether (bellwether.markets)

Normalizes Kalshi and Polymarket markets, prices and volumes into one schema, and matches same-event contracts across both venues with price spreads.

- Atlas card: https://inite.ai/en/atlas/bellwether.markets
- Site: https://bellwether.markets
- For: Independent developers and AI agents building on Kalshi and Polymarket prediction market data
- Use 0/100 · alive 100/100

## Used for

- find price spreads for the same event across Kalshi and Polymarket
- list and search open markets across both venues
- let AI agents query markets and spreads via MCP tools

## Price

- from 49 USD/month, free plan (read 2026-10-26 on https://bellwether.markets/#pricing)

## For developers

- OpenAPI: https://bellwether.markets/openapi.json (4 paths)
- API docs: https://bellwether.markets/docs
- MCP server: markets.bellwether/prediction-markets (namespace; open on 2026-10-26, 3 tools)
- Read 2026-10-26

## MCP server, measured daily

Server: https://api.bellwether.markets/mcp, checked every day since 2026-10-26 (2 checks).

- Answered: measuring, 2 daily checks so far
- Median first answer: 499 ms
- Sign-in: none
- Context its tool definitions take: about 241 tokens (3 tools)
- Tool definitions: C, 67/100
- Failing "params_described": 3 of 3 tools
- Failing "annotations": 3 of 3 tools
- Method: https://inite.ai/en/atlas/mcp/report

## Your data

- Certifications stated: none
- Read 2026-10-26

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Source: INITE Atlas, https://inite.ai/en/atlas/bellwether.markets. JSON: https://inite.ai/api/atlas/bellwether.markets. MCP: https://inite.ai/api/mcp (atlas_lookup).