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Event: close_to_bond
Cost: 0.2 credits per delivery
The close_to_bond callback fires when a trade occurs at the near-certain end of a market (for example an outcome trading at ≥ 95¢ or ≤ 5¢). The full callback schema is in the auto-generated Close to bond callback reference; this page explains the one part the schema can’t show on its own: how the price filters define the zone.

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Defining the bond zone

The bond zone is defined entirely by how you combine min_price and max_price. The relationship between the two values selects one of four modes:
min < max is a band, not a bond. If you set min_price: 0.75 and max_price: 0.90, you do not get “fires above 90% or below 75%”. Because min < max, it switches to bounded-range mode and fires only when the price lands inside the 75–90% band. To alert on the two near-certain extremes, you must set min > max (see below).

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Alerting on near-certain outcomes

To get notified when an outcome becomes near-certain in either direction (at or above 90% or at or below 10%), set min_price higher than max_price:
Because 0.90 > 0.10, this is read as two separate edges. A trade at 96¢ fires with bond_side: "high"; a trade at 4¢ fires with bond_side: "low". For a single edge, set just one of the two.

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How price is read

  • The traded position’s own price is used: the price of the exact outcome token (position_id) that printed.
  • Trades at a price of exactly 0 or 1 are skipped, since there is no remaining risk to alert on.
  • price is on a 0.0–1.0 scale (so 95¢ = 0.95).

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Picking the right side

On a binary market, “YES at ≤10%” and “NO at ≥90%” are the same event priced from opposite tokens. If you add position_outcome_indices: [0] you will only ever see trades that print on the Yes/Up token (index 0); trades on the No token (index 1) won’t fire even when they hit the same bond zone. Omit position_outcome_indices to catch the zone regardless of which side the trade prints on.

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Subscription filters

Add these to the filters object when you create the subscription. At least one of min_price or max_price is required.
Scope by market taxonomy. tags matches a market’s own tags or its category, given as the display label shown on Polymarket (for example "Sports", "Politics", or "FIFA World Cup"), not a slug. series_slugs matches the market’s parent series by slug (for example "nba-finals"). Both are case-insensitive, accept up to 500 values each, and an empty or omitted list applies no taxonomy restriction.
For a worked walkthrough across both webhooks and websockets, see the Bond-zone alerts guide.
Last modified on July 13, 2026