Strule

Strule is a compact JSON format for portable, user-configurable string rules. It supports common string, numeric, and length predicates with AND, OR, and negation. Rules contain no regular expressions, functions, or executable code.

Example

Open the URL search-param rule builder to configure rules, test a URL, and inspect the generated schema.

Install

npm add @strule/core
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Define a Strule value

An AnyOf contains one or more AllOf arrays. The outer array is OR; adjacent operator and operand pairs within each inner array are AND.

const accessRule = [
  ["=", "admin"],
  ["^=", "org_", "$=", "_prod", "#>=", 10],
];
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This value matches "admin" or a string that starts with "org_", ends with "_prod", and contains at least 10 Unicode code points.

See the Strule Specification for the complete syntax, numeric model, Unicode requirements, and validity rules.

Match strings

Use matches for a single value:

import { matches } from "@strule/core";

matches(accessRule, "admin"); // true
matches(accessRule, "org_team_prod"); // true
matches(accessRule, "owner"); // false
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Use compile when matching many values against the same configuration. Compilation validates and snapshots the configuration once.

import { compile } from "@strule/core";

const isAllowed = compile(accessRule);

isAllowed("admin");
isAllowed("org_team_prod");
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matches and compile throw InvalidStruleError when the configuration is invalid. The error exposes the same structured issues returned by validate.

import { InvalidStruleError, compile } from "@strule/core";

try {
  compile([[">", "10"]]);
} catch (error) {
  if (error instanceof InvalidStruleError) {
    console.error(error.issues);
  }
}
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Validate configuration

Use validate for JSON, stored configuration, and editor state that must report errors without throwing.

import { validate } from "@strule/core";

const result = validate(JSON.parse(source));

if (result.ok) {
  console.log(result.value);
} else {
  for (const issue of result.issues) {
    console.error(issue.code, issue.path, issue.message);
  }
}
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Each issue includes a stable code, an array-index path, the expected input, the received value, and a default English message.

Validate an editor field

validatePredicate checks one operator and operand without requiring a complete AnyOf. This is useful while editing one predicate in a UI.

import { validatePredicate } from "@strule/core";

const result = validatePredicate(">", "number");

if (!result.ok) {
  // [{ code: "invalid_type", path: [1], ... }]
  showFieldErrors(result.issues);
}
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Use baseOperators to populate an operator selector and getOperandKind to choose an input control.

import { baseOperators, getOperandKind } from "@strule/core";

baseOperators; // ["=", "^=", ..., "#<="]
getOperandKind("!>="); // "number"
getOperandKind("#<="); // "length"
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Negation does not change the operand kind.