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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 probability filters define the zone.

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Defining the bond zone

The bond zone is defined entirely by how you combine min_probability and max_probability. The relationship between the two values selects one of four modes:
You setModeFires whenbond_side
min_probability onlySingle high edgeprobability ≥ min_probability"high"
max_probability onlySingle low edgeprobability ≤ max_probability"low"
Both, with min < maxBounded rangemin_probability ≤ probability ≤ max_probability"high"
Both, with min > maxTwo edgesprobability ≥ min_probability or probability ≤ max_probability"high" or "low"
min < max is a band, not a bond. If you set min_probability: 0.75 and max_probability: 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 probability 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 — trading at or above 90% or at or below 10% — set min_probability higher than max_probability: 
{
  "min_probability": 0.90,
  "max_probability": 0.10
}
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 probability is read

  • The trade’s probability is used when present; otherwise its price is used as the probability.
  • Trades with a probability of exactly 0 or 1 are skipped — there is no remaining risk to alert on.
  • probability and price are 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_probability or max_probability is required.
FilterTypeDescription
min_probabilitynumberHigh-edge / lower bound of the zone, 0.0–1.0.
max_probabilitynumberLow-edge / upper bound of the zone, 0.0–1.0.
condition_idsstring[]Restrict to specific markets (max 500).
position_idsstring[]Restrict to specific outcome tokens (max 500).
outcomesstring[]Restrict by outcome name, e.g. ["Yes", "No"] (max 500).
position_outcome_indicesnumber[]Restrict by outcome index: 0 (Yes/Up) or 1 (No).
event_slugsstring[]Restrict to specific events (max 500).
exclude_shortterm_marketsbooleanExclude short-term Up/Down markets.
For a worked walkthrough across both webhooks and websockets, see the Bond-zone alerts guide.
Last modified on June 5, 2026