> ## Documentation Index > Fetch the complete documentation index at: https://docs.stackra.figentra.com/llms.txt > Use this file to discover all available pages before exploring further. # 0331 — @stackra/rules: one condition engine for every rule consumer > Accepted · 2026-10-24 ## Context Several features need the same thing: a test over facts about a customer, a cart, a record or an order history, which yields a yes or a no and a reason for the answer. Segments, discounts and promotions, pricing rules, related-product rules, automations and visibility rules all need one. Without a shared engine, each consumer would write its own evaluator, with its own operators and its own reading of a missing value, and one rule could give different answers in two places. A rule that a tenant writes is data that references registered code, which [0227](https://docs.stackra.figentra.com/adr/0227-rejected-and-deferred-technologies-refreshed.md) allows, and it never carries logic of its own ([0154](https://docs.stackra.figentra.com/adr/0154-tenant-code-runs-only-in-a-sandboxed-code-step.md)). The owner decided the shape in the final structure review of 2026-10-24. ## Decision 1. **One engine.** `@stackra/rules` is a free framework package in the `application` category ([0127](https://docs.stackra.figentra.com/adr/0127-package-categories-including-infrastructure.md)). It evaluates conditions for every rule consumer. A consumer never builds an evaluator of its own. 2. **Condition tree.** A condition is a tree of `all`, `any` and `not` nodes. Its leaves test one field with one operator against a value. 3. **Typed operators.** Each field type has an operator set that the engine fixes: string, number, money ([0220](https://docs.stackra.figentra.com/adr/0220-stackra-money-and-the-ledger-package.md)), date, enum, list and geo. A consumer chooses fields, and it does not choose operators. 4. **Fact sources.** Each consumer registers a fact source, which is a typed description of the fields its rules may test. Examples are customer attributes, cart totals, order history aggregates and record fields. The engine knows no commerce. A field that no fact source registers cannot be tested. 5. **Versioned rule sets.** A rule set is a model that carries revisions (`HasRevisions`, [0321](https://docs.stackra.figentra.com/adr/0321-the-trait-inventory-owning-packages-and-schedulable.md)). An evaluation runs against one stated revision, and its explanation names that revision. 6. **Deterministic evaluation.** The same facts and the same revision give the same result. The current time is a fact that the caller supplies, and the engine does not read a clock. 7. **Explanation.** Every result says which condition matched or failed, by its path in the tree. 8. **Rule builder.** The package ships a rule-builder panel component in its `react` entry. The panel offers only the registered fields and the operators of their types. 9. **Consumers own the outcome.** The engine returns a result and nothing more. What a match does belongs to the consumer: * segments ([0332](https://docs.stackra.figentra.com/adr/0332-stackra-segments-audiences-defined-by-rules.md)) record membership; * discounts and promotions apply a discount; * pricing rules choose a price, and pricing owns markets ([0244](https://docs.stackra.figentra.com/adr/0244-markets-owned-by-pricing.md)); * related-product rules rank through search ([0221](https://docs.stackra.figentra.com/adr/0221-search-postgres-hybrid-elasticsuite-parity-arabic-and-operations.md)); * automations trigger a workflow. 10. **Tenant data, never code.** A rule is tenant data that references only registered fields and operators. That is the data-that-references-registered-code case of [0227](https://docs.stackra.figentra.com/adr/0227-rejected-and-deferred-technologies-refreshed.md). It is not an expression language. Arbitrary logic runs only in the sandboxed code step of [0154](https://docs.stackra.figentra.com/adr/0154-tenant-code-runs-only-in-a-sandboxed-code-step.md). 11. **IAM conditions.** IAM conditions ([0208](https://docs.stackra.figentra.com/adr/0208-iam-model-scope-tree-roles-conditions-deny-delegation-and-permission-names.md)) may reuse the operator set. The IAM policy decision point keeps its own evaluation path, for performance and security. 12. **Entries.** The package has the `contracts`, `core`, `node` and `react` entries. It adds `config` and `testing` where it needs them, as [0294](https://docs.stackra.figentra.com/adr/0294-programming-model-v3-grammar-folders-identities-and-naming.md) decision 15 allows. ## Consequences * A consumer gets evaluation, explanation and versioning without writing them, and two consumers that test the same field get the same answer. * A tenant cannot test a field that no fact source registers. Adding a field to a rule is a change that the owner of the consumer makes in code. * Adding an operator is a change to the engine, and no consumer changes with it. * A rule that a tenant writes is versioned, explained and unable to run code. ## Enforcement * planned — gen check: a rule set that names an unregistered field, or an operator outside the operator set of its field type, fails. * planned — tests in `@stackra/rules`: determinism for a fixed revision and fixed facts, and an explanation that names the matched or failed path. * planned — an oxlint boundary rule: no evaluator of condition trees outside `@stackra/rules`, and no dynamic code evaluation in the package. ## Supersedes and sources Supersedes: none. Builds on [0127](https://docs.stackra.figentra.com/adr/0127-package-categories-including-infrastructure.md), [0154](https://docs.stackra.figentra.com/adr/0154-tenant-code-runs-only-in-a-sandboxed-code-step.md), [0220](https://docs.stackra.figentra.com/adr/0220-stackra-money-and-the-ledger-package.md), [0227](https://docs.stackra.figentra.com/adr/0227-rejected-and-deferred-technologies-refreshed.md), [0244](https://docs.stackra.figentra.com/adr/0244-markets-owned-by-pricing.md) and [0321](https://docs.stackra.figentra.com/adr/0321-the-trait-inventory-owning-packages-and-schedulable.md). Keeps the evaluation path of the IAM decision point in [0208](https://docs.stackra.figentra.com/adr/0208-iam-model-scope-tree-roles-conditions-deny-delegation-and-permission-names.md). Sources: the owner's final structure review of 2026-10-24, restated in this ADR's own words. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.