Adjacent

What it is

A REST API over Kalshi and Polymarket, plus a layer of derived series on top of it that nobody else in this catalogue publishes: 64 indices in the public catalog, a set of cross-venue reference rates, and a stored news and CFTC-filings corpus linked back to the markets each item touches.

The raw half is conventional. Markets, events, trades, quotes and OHLC candles arrive in one schema, with every id prefixed by its venue (kalshi:, polymarket:) so a list response feeds a detail or history call without rebuilding a ticker. Prices are on a 0-100 scale, so 75 is an implied probability of 75%.

The derived half is the reason to look. An index combines many markets into one level — the political indices run on a 50-150 scale where the value minus 50 is the implied win probability in percent, and RED and BLUE are composites of presidential, Senate, House, gubernatorial and mayoral sub-indices at fixed weights of 40/30/20/8/2. A reference rate takes the same underlying question priced on more than one venue, or a contract that rolls into its successor, and returns one series plus the spread between its sources, weighted by volume, equally, or by median. Constituent and source endpoints show what moved the number, which is the part a chart alone cannot tell you.

The vendor previously operated as Adjacent News on adj.news; that domain now redirects to the current one.

Availability

A data API with no geographic gate on the public tier: the anonymous endpoints answer without a token or an account, and paid access is bought with a card rather than an identity check. There is no KYC step because there is nothing to deposit.

What there also is, as of 19 September 2026, is no terms of service, privacy policy or legal page of any kind — /terms, /legal and /privacy each answer 200 with the site's landing page, byte for byte the same document a nonsense path is served. The usage rules that do exist are in the pricing and rate-limit documentation, which is where the redistribution restriction below comes from. Anyone who needs a contract before building on a data source should treat that as the blocker it is.

Pricing

Three published plans. Free is $0 and covers the public API and MCP at a 15-minute delay, limited at the edge to 50 requests per 10 seconds per IP. Pro is $50 a month for realtime indices, rates, markets, history and MCP, with 5 seats, 30 requests a minute and 20,000 a day. Premium is $250 a month for the same data with 10 seats, 180 requests a minute and 150,000 a day.

Paid limits are organization-wide and reset at 00:00 UTC, so extra API keys buy no throughput, and an organization runs at most 4 requests at a time. The free price endpoints are capped by history as well as by rate: hourly buckets for the previous 30 days, or daily buckets for the previous 90. Finer intervals and anything deeper are paid.

Two exclusions are stated on the pricing page rather than buried: neither paid plan permits redistribution or use in a financial product, and WebSockets, the index builder and ratings data are not part of the v1 plans at all.

Markets & resolution

Kalshi and Polymarket only — and on the free tier, in practice, Kalshi alone. In the public catalog on 19 September 2026 that is 64 indices — the political set plus NFL team indices — and 1,694 markets, every one of them Kalshi, split between elections and sports. Adjacent resolves nothing itself: it reads prices from the two venues, and settlement, disputes and payout are the venues' business, which is why resolution_source on this card is null.

The settlement field can hold one value and the two covered venues do not share one: Kalshi settles event contracts in dollars, Polymarket in USDC on-chain. The card says cash because that is what the public tier returns; read it as a property of the underlying venues rather than of the API.

Two derived series deserve a caution that the docs give themselves. A reference rate's spread is the distance between its sources, and a wide one means the single number is hiding a disagreement rather than summarising one. Related news results are ranked matches, not evidence that an article moved a price.

Integrations

REST over https://api.adjacent.markets with an /api/v1/ prefix, a bearer token or api_key query parameter for the realtime tier, and scoped API keys created in the app. The keyless tier is a separate path rather than the same one unauthenticated: /api/v1/public/markets answers, while /api/v1/markets returns 401. Exports of events, markets, indices and rates come back as CSV or TSV, up to 10,000 rows per request.

There is an MCP server at mcp.adjacent.markets with four tools — list, find, get and price — which answers without a key at the 15-minute delay and takes an apiKey query parameter for realtime. Adjacent also runs a SEDA data proxy for on-chain consumers; the testnet host is ungated and delayed, and the mainnet one is documented as not generally available.

No first-party Python or JavaScript SDK is documented, and no WebSocket. This is a polling API.

Limitations

Two venues. A reader who wants Limitless, Myriad or Manifold in the same schema is at the wrong card — and on the free tier it is one venue, not two. Every market the public endpoints returned on 19 September 2026 was Kalshi, and filtering them to Polymarket returned nothing, so the tier a reader can check for free does not demonstrate the coverage the paid one is bought for.

No WebSocket on any published plan, so realtime means polling inside 30 or 180 requests a minute with four concurrent slots. No redistribution and no use in a financial product on either paid plan, which rules out most of what a data licence is normally bought for and leaves research, internal tooling and agents.

The indices are the product, and they are also a methodology you are trusting: fixed composite weights, a UPFI factor set inside the sub-indices, and a 50-150 scale that is not a probability until you subtract 50. Check an index's constituents before quoting its level at anyone.

And the absent legal pages cut both ways — there is no terms document setting out uptime, notice of breaking changes, or what happens to your access if the vendor's own upstream agreement with a venue changes.

Alternatives

FinFeedAPI covers nine venues instead of two and sells usage credits rather than seats, but ships no indices or news. Dome covered Kalshi and Polymarket with deeper order-book history; Polymarket acquired it in February 2026 and its documentation sets end of life for the Dome APIs at 28 April 2026. Going straight to the venues' own APIs costs nothing and gives you full depth and streaming, at the price of writing the normalisation and the index arithmetic yourself.