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Standard Predicates

Predicates are the building blocks for contract rules. They evaluate based on commit data and contract state.

Path Predicates​

modifies​

Checks if the commit writes to paths under a given prefix.

+modifies(/members)

Arguments:

  • path — Path prefix to check

Behavior:

  • Returns true if any path in the commit body starts with the given prefix
  • Used for path-based access control rules

Example:

// Only allow membership changes if all members sign
always (+modifies(/members) implies +all_signed(/members))

Signature Predicates​

signed_by​

Verifies the commit is signed by a specific ed25519 key.

signed_by(/users/alice.id)

Arguments:

  • path — Path to the public key in contract state

any_signed​

Verifies at least one member from a path has signed.

+any_signed(/members)

Arguments:

  • path — Path prefix containing member public keys

Behavior:

  • Enumerates all .id files under the path
  • Passes if ANY member has a valid signature
  • Used for "any member can act" patterns

all_signed​

Verifies ALL members from a path have signed.

+all_signed(/members)

Arguments:

  • path — Path prefix containing member public keys

Behavior:

  • Enumerates all .id files under the path
  • Passes only if EVERY member has a valid signature
  • Used for "unanimous consent" patterns like adding members

threshold​

n-of-m multisig verification.

threshold(2, /treasury/signers)

Arguments:

  • n — Minimum signatures required
  • signers_path — Path to JSON array of authorized signer paths

Features:

  • Prevents same signer from signing twice
  • Rejects unauthorized signers
  • Works with any n-of-m configuration

Time Predicates​

before​

Checks current time is before a deadline.

before(/deadlines/expiry.datetime)

after​

Checks current time is after a timestamp.

after(/deadlines/start.datetime)

State Predicates​

bool_true / bool_false​

Check boolean state values.

bool_true(/status/delivered.bool)
bool_false(/flags/cancelled.bool)

text_eq​

Compare text values.

text_eq(/status.text, "approved")

num_eq / num_gt / num_gte / num_lt / num_lte​

Numeric comparisons.

num_gte(/balance.num, 100)
num_lt(/deposit.num, /limit.num)

Oracle Predicates​

oracle_attests​

Verifies a signed attestation from a trusted oracle.

oracle_attests(/oracles/delivery.id, "delivered", "true")

Arguments:

  • oracle_path — Path to oracle's public key
  • claim — The claim type being attested
  • value — Expected value (optional)

Security features:

  • Verifies oracle signature
  • Enforces attestation freshness
  • Binds attestation to specific contract
  • Prevents replay attacks

Hash Predicates​

hash_matches​

Verifies SHA256 hash commitment.

hash_matches(/commitments/secret.hash, /revealed/value.text)

Using Predicates in Rules​

Predicates are combined with logical operators in rule formulas:

export default rule {
  starting_at $PARENT
  formula {
    // All commits must be signed by alice OR bob
    signed_by(/users/alice.id) | signed_by(/users/bob.id)
  }
}

export default rule {
  starting_at $PARENT
  formula {
    // After deadline, only buyer can commit
    after(/deadlines/expiry.datetime) -> signed_by(/users/buyer.id)
  }
}

export default rule {
  starting_at $PARENT
  formula {
    // 2-of-3 multisig required
    threshold(2, /treasury/signers)
  }
}

Custom WASM Predicates​

You can create custom predicates as WASM modules:

modal predicate create --name my_predicate --output ./predicates/

Then reference in contracts:

wasm(/predicates/my_predicate.wasm, arg1, arg2)