Best Polymarket Order Book API

The ranking rewards whoever does the specific job best, not whoever has the most features. The full matrix that underpins it covers 10 providers across historical prices, historical L2, resolution, free tiers, and bulk export. Facts below were verified against public pricing and docs pages on September 24, 2026, and recorded in our provider matrix.

• 1. PolyOrderbooks — for a REST API that queries full bid/ask ladders at a documented 250ms grid through paid windows to 30–120 days, using calendar-time resolution parameters.
• 2. Official Polymarket APIs — for the current book of any market via GET /book — free, authoritative, and live, but with no documented arbitrary historical full-L2 endpoint.
• 3. PolymarketData — for timestamped L2 snapshots at a documented 1-minute resolution and time-based query parameters.
• 4. Telonex — for event-driven book snapshot channels (5, 25, and full) delivered as downloadable Parquet rather than continuous REST query.
• 5. DepthFeed — for event-driven full-depth snapshots with downsampling from 1 second to 1 day on paid plans.
• 6. Predexon — for order book history REST endpoints that are free and unlimited on all plans.
• 7. PolyTest — for point-in-time snapshot lookup with a documented 8-level depth model for Up/Down backtests.

Measured coverage is the part a marketing page cannot answer. Our archive captures order books every 250ms and serves every plan, including free Starter, at that same 250ms query resolution. Competitors in the matrix cap documented L2 detail at 1-minute (PolymarketData), at 8 levels per snapshot (PolyTest), or rely on self-reported sub-second claims that conflict across their own pages (PolyTest, PolyBackTest). Resolution is not the only axis. Read the matrix row for interval-sampled versus event-driven capture (Telonex, DepthFeed), for on-chain-only limits that exclude the off-chain book entirely (Dune), and for archives that stop at coverage end or endpoint shutdown (polyReplay, Dome). Each listed product is the best answer for a specific job, and none is the best answer for every job.

Free tiers matter when the honest answer is the official API — which it usually is for live prices. Every provider in the matrix lists its free tier; where the free tier is only a sample or a trial, the row says so. If the job is historical depth, expect to pay for it, because depth history is the expensive thing to keep.

An order-book API for this venue is a three-part contract: a snapshot with the full ladder and both sides, a stream that keeps the snapshot current across reprises, and historical snapshots by UTC second. The ranking above separates products on the second and third parts, because live-only feeds miss the diagnostic moment.

Test the boundary case: subscribe across a repricing second and see whether the stream preserves the ordering where the executable side empties first and the bound moves after. The providers that keep the side information intact are the ones your logic can trust.

The archive-backed snapshot is what turns an order-book API from a feed into a research tool; with it, any past second can be replayed, which is why the archive pages and this list point at the same stack.

When comparing order-book providers, add one behavioral test to the checklist: replay the same repricing second through both and ask which one preserves the ordering of side, floor, and bound. The loser is often silently computing the display mid.

Verify you can reconstruct the one-sided frame from the stream alone, since that is the venue's most common state.

Check the snapshot-to-stream merge latency in seconds, not in marketing language; a slow merge breaks every backtest.

Keep the historical snapshot endpoint in scope even if live is your only need today; you will need it the first time you audit a fill.

• Full provider matrix
• Order book data
• Price history
• Data download