TYPE 0x0303 · COVENANT FAMILY

AMOUNT_LOCK

Output amount range check. Verifies that the output value falls within a committed minimum and maximum range: min_sats ≤ output_amount ≤ max_sats. No witness data required — the output amount is read directly from the transaction context.

Covenant Invertible

Ladder Diagram

Fields

Field	Data Type	Size	Side	Description
min_sats	NUMERIC	1-4 B	Conditions	Minimum output amount in satoshis (inclusive). Decoded as int64; the evaluator does not reject negative values, but a negative `min_sats` simply broadens the lower bound.
max_sats	NUMERIC	1-4 B	Conditions	Maximum output amount in satoshis (inclusive). Decoded as int64. If `max_sats < min_sats` the range is empty and every spend returns UNSATISFIED — a deliberate "always-fail" composes via the inverted flag.

No witness fields required — the output amount is read directly from the spending transaction context.

Wire Format Breakdown

0x0303 0 2 NUMERIC · 3B NUMERIC · 3B Conditions = 14 bytes

0x0303 0 0 Witness = 4 bytes (empty block)

Total 20 bytes

Evaluation Logic

1.Collect all NUMERIC fields. If fewer than 2 → ERROR. The first is min_sats, the second is max_sats.

2.ReadNumeric on both. If either is undecodable → ERROR. Both are stored as int64; no sign or ordering check is performed.

3.Compare: ctx.output_amount ≥ min_sats && ctx.output_amount ≤ max_sats. If true → SATISFIED; otherwise → UNSATISFIED

Return Values

Condition	Result
Fewer than 2 NUMERIC fields	ERROR
Either NUMERIC undecodable	ERROR
`output_amount < min_sats`	UNSATISFIED
`output_amount > max_sats`	UNSATISFIED
`min_sats ≤ output_amount ≤ max_sats`	SATISFIED

JSON Wire Format

Conditions (min 10,000 sats, max 1,000,000 sats)

{
  "type": "AMOUNT_LOCK",
  "inverted": false,
  "fields": [
    { "type": "NUMERIC", "value": 10000 },
    { "type": "NUMERIC", "value": 1000000 }
  ]
}

This constrains the output to carry between 10,000 and 1,000,000 satoshis. Outputs below the minimum (including dust) or above the maximum are rejected.

Worked Example

min_sats = 10,000, max_sats = 1,000,000

Output of 546 sats: 546 < 10,000 → UNSATISFIED (dust rejected)

Output of 10,000 sats: 10,000 ≥ 10,000 and ≤ 1,000,000 → SATISFIED (boundary)

Output of 500,000 sats: within range → SATISFIED

Output of 1,000,000 sats: 1,000,000 ≤ 1,000,000 → SATISFIED (boundary)

Output of 5,000,000 sats: 5,000,000 > 1,000,000 → UNSATISFIED

Use Cases

Minimum Output Enforcement

Prevent creation of economically unspendable outputs by setting a minimum above the dust threshold. Useful for protocols that need outputs to remain spendable without excessive fee ratios.

Dust Prevention

Exchanges and payment processors can enforce minimum withdrawal amounts at the script level, preventing users from creating dust UTXOs that bloat the UTXO set and cost more in fees than they are worth.

Value Range Constraints

Limit maximum output value for per-transaction spending caps. Combined with other covenant blocks, this enables spending policies like "hot wallet can move at most 0.01 BTC per transaction" without custodial intermediaries.

Inverted: Value Exclusion Zones

With the inverted flag, the block rejects outputs within the range — useful for excluding specific value bands. For example, preventing outputs in a range known to correlate with specific payment amounts for privacy reasons.

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