decide.fyi Decision API

Deterministic Decision API engine powering workflow applications, stable MCP notary remotes, decision memo packets, and execution gates

Positioning: Decide is the API engine and compatibility surface. Krafthaus workflow apps, Policy MCP Notaries, decision memo packets, and execution gates are application surfaces that reuse the same verdict, request ID, and evidence contract.

Production Determinism Boundary

Binding production verdicts should use a versioned declarative rulebook:

Runtime architecture: see docs/RULEBOOK_RUNTIME_ARCHITECTURE.md. Machine-readable schema: https://api.decide.fyi/schemas/rulebook-v1.schema.json. Active runtime manifest: https://api.decide.fyi/manifests/rulebook-runtime-v1.json. Downstream application binding: decide_application_binding_v1.

The production core is hybrid_declarative_rulebook_with_trusted_adapters: direct declarative rulebooks are supported, registered first-party trusted adapters may supply bounded facts, and customer executable rulebooks are rejected. In both supported binding modes, Rulebook v1 remains the only binding verdict selector.

{
  "mode": "rulebook",
  "rulebook": {
    "schema_version": "rulebook_v1",
    "rulebook_id": "pricing_exception",
    "version": "2026-06-11",
    "input_schema": {
      "required": ["discount_percent"],
      "properties": {
        "discount_percent": { "type": "number" }
      }
    },
    "rules": [
      {
        "rule_id": "approve_standard_discount",
        "priority": 50,
        "condition": {
          "field": "discount_percent",
          "operator": "lte",
          "value": 15
        },
        "outcome": {
          "decision": "yes",
          "verdict": "APPROVE",
          "action": "approve_discount",
          "reason_code": "WITHIN_STANDARD_LIMIT"
        }
      }
    ],
    "default_outcome": {
      "decision": "review",
      "verdict": "REVIEW",
      "action": "route_to_owner",
      "reason_code": "NO_RULE_MATCHED"
    }
  },
  "context": {
    "inputs": {
      "discount_percent": 10
    }
  }
}

mode: "rulebook" does not call an LLM. It validates the request rulebook against the published JSON Schema, hashes the rulebook, evaluates bounded conditions, and returns yes, no, or review alongside the application verdict, action, reason code, matched rule, and evaluator_version. Responses also include rulebook_contract with the enforced schema URL/hash, runtime_binding with the direct or trusted-adapter binding mode, input_hash, a SHA-256 hash of the canonical inputs or adapter facts consumed by the declarative evaluator, plus a rulebook_attestation_v1 bundle hash over the deterministic execution tuple. Production deployments can sign that bundle hash with a rulebook_attestation_signature_v1 Ed25519 envelope; verification keys are published at /.well-known/rulebook-attestation-keys.json. Set DECIDE_RULEBOOK_ATTESTATION_SIGNATURE_REQUIRED=true in production to fail closed instead of returning unsigned Rulebook decisions. Publish retired public verification keys with DECIDE_RULEBOOK_ATTESTATION_KEY_HISTORY_JSON so older Decision Records remain verifiable after rotation.

Rulebook requests cannot preload Decide-generated Decision Record material. Fields such as runtime_binding, trusted_adapter, adapter_facts, rulebook_attestation, application_verdict, and action are response-only at the request body, context.inputs, and adapter-facts boundaries; attempts return `RULE

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