REST API / Polymarket / Open Interest

Open Interest (Polymarket)

Current open interest for a Polymarket market — the total value of outstanding positions — returned as a point-in-time snapshot.

GET/v2/polymarket/markets/{condition_id}/open_interest

Query Parameters

condition_idstring (path)Required

Polymarket condition ID (path parameter).

Response Schema

condition_idstring

The requested condition ID.

seriesobject[]

OI snapshots over time. Currently a single-point series (latest snapshot only) when data is present, or empty when no OI is captured for this market.

tinteger

Snapshot capture timestamp (unix seconds).

total_open_interestnumber

Sum of OI across all outcomes.

by_outcomeobject[]

OI broken down per outcome.

outcome_namestring

Internal outcome name.

outcome_labelstring

Display label.

open_interestnumber

OI for this outcome at the snapshot time.

_metaobject

Data warning metadata.

data_available_fromnull

null — no historical OI series available.

snapshot_onlyboolean

true — the series contains only the current snapshot, not real history.

warningstring

Plain-text caveat about the data state.

Error Responses

All errors return the same envelope. The code field is stable and programmatically branchable; error and message are human-readable. errors[] is present only on validation failures with field-level detail. See the full error code reference →

successboolean

Always `false` on error responses.

errorstring

Short, human-readable title (e.g. 'Invalid API Key.').

messagestring

Human-readable explanation for the error. Safe to surface in UIs.

codestring

Stable, hierarchical machine-readable code (e.g. 'validation.invalid_enum'). Use for programmatic handling.

doc_urlstring

Link to this code's entry in the Error Reference.

errorsobject[]

Optional. Present only on validation failures with field-level detail.

fieldstring

Name of the offending parameter.

codestring

Field-level machine code.

messagestring

Human-readable explanation.

Authentication

API Key

To secure your requests, we strongly recommend passing your API key via the X-API-Key header. This prevents sensitive keys from being exposed in access logs or browser history.

Request HeaderX-API-Key: pmx_test_5e8f...

Rate Limits

API rate limits are enforced based on the tier associated with your API key. Limits are tracked on two dimensions: requests per second and requests per month. Each completed request counts toward the global monthly quota. Separate endpoint-group monthly limits (matched markets, arbitrage, EV) only advance when the response body has success: true.

Usage is returned on responses via headers such as:

Response Headers (global)X-RateLimit-Limit-Second: 10X-RateLimit-Remaining-Second: 9X-RateLimit-Limit-Month: 1000X-RateLimit-Remaining-Month: 842Example (endpoint-group, when applicable)X-RateLimit-Limit-Arb-Month: 500X-RateLimit-Remaining-Arb-Month: 412

If you exceed a rate limit, the API returns a 429 status with a Retry-After header indicating when you can resume.

Request

Live API Key

Demo Mode

Verified

Parameters

Condition IDRequired

Response

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