JSONLogic Validator

Implement and validate JSONLogic rules—portable, JSON-serializable business logic that works across JavaScript, Python, PHP, Ruby, Go, Java, .Net, and C++.

Core Syntax

Every rule: { "operator": [arguments] }

{"==": [1, 1]}                              // comparison
{"var": "user.name"}                        // data access
{"and": [{">=": [{"var": "age"}, 18]}, {"var": "active"}]}  // compound

Quick Reference

Workflow

1. Gather Requirements

Clarify:

• What data fields are available?
• What conditions determine the outcome?
• What should the rule return (boolean, value, category)?

2. Write the Rule

Build incrementally from inner expressions outward:

// Requirement: "Premium users over 25 get 20% discount, others get 10%"
{
  "if": [
    {"and": [
      {"==": [{"var": "tier"}, "premium"]},
      {">": [{"var": "age"}, 25]}
    ]},
    0.20,
    0.10
  ]
}

3. Validate

Run the validation script (no dependencies required):

node scripts/validate-jsonlogic.js '<rule>' '<data>'

Example:

node scripts/validate-jsonlogic.js '{">=": [{"var": "age"}, 18]}' '{"age": 25}'

4. Test with Cases

Requires: npm install json-logic-js

node scripts/test-jsonlogic.js '<rule>' --test-cases '[
  {"data": {"age": 25}, "expected": true},
  {"data": {"age": 15}, "expected": false}
]'

Common Patterns

Null-safe access with default

{"var": ["user.name", "Guest"]}

Range check (between)

{"<=": [0, {"var": "value"}, 100]}

Multi-condition (all must pass)

{"and": [
  {">=": [{"var": "age"}, 18]},
  {"==": [{"var": "status"}, "active"]},
  {"in": [{"var": "role"}, ["admin", "editor"]]}
]}

Grade/tier classification

{"if": [
  {">=": [{"var": "score"}, 90]}, "A",
  {">=": [{"var": "score"}, 80]}, "B",
  {">=": [{"var": "score"}, 70]}, "C",
  "F"
]}

Array operations

// Sum: reduce with +
{"reduce": [{"var": "items"}, {"+": [{"var": "accumulator"}, {"var": "current"}]}, 0]}

// Filter: keep matching
{"filter": [{"var": "items"}, {">": [{"var": ""}, 10]}]}

// Any match: some
{"some": [{"var": "items"}, {"==": [{"var": ".status"}, "error"]}]}

Truthy/Falsy (differs from JavaScript)

Falsy: 0, [], "", null Truthy: Everything else (including "0" and [0])

Validation Checklist

Before deploying a rule:

• Valid JSON syntax
• All operators spelled correctly
• Arguments in arrays where required
• Data paths match actual data structure
• Edge cases handled (null, empty, missing keys)
• Tested with representative data samples

References

For complete operator documentation with all arguments and edge cases:

• See references/jsonlogic-reference.md