Define your business rules, then generate JSON that violates exactly one constraint — test specific failure modes deterministically.
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In short: A constraint-violation sandbox lets you define the rules your data must follow — types, ranges, lengths, required fields, enums — then generates JSON that breaks exactly one of those rules while keeping everything else valid. RealJSON's sandbox does this entirely in your browser, so you can test each validation failure mode in isolation and deterministically.
A constraint-violation sandbox lets you define the rules your JSON data must follow — field types, numeric ranges, string lengths, required fields, allowed enum values — and then generates test data that breaks exactly one of those rules while satisfying all others. This isolates specific failure modes, letting you test precisely how your system handles each type of invalid input.
Unlike random chaos injection, constraint-violation testing is deterministic and domain-aware. If you're building a structural engineering app, you can define that beam_span must be between 3 and 15 meters, then generate a payload where it's 2.9 meters — testing exactly that edge case without affecting any other field.
Field must be present. Violation: field is deleted from the output.
Field cannot be null. Violation: field is set to null.
Value must be a string. Violation: replaced with a number.
Value must be a number. Violation: replaced with a non-numeric string.
Value must be true or false. Violation: replaced with the string "true_string".
Value must be an array. Violation: replaced with an object.
Number must be ≥ X. Violation: set to X−1.
Number must be ≤ X. Violation: set to X+1.
String must have ≥ X characters. Violation: string shortened to X−1 characters.
String must have ≤ X characters. Violation: string padded to X+50 characters.
Value must be in a defined list. Violation: replaced with an unlisted sentinel string.
String must match a regex. Violation: replaced with a pattern-breaking string.
When you violate multiple constraints at once, it becomes impossible to know which violation caused the failure. Single-constraint violation testing follows the scientific principle of changing one variable at a time. Your validation layer should return a specific error for a specific violation — this tool generates the exact input that should trigger each individual error message.
This approach is essential for domain-specific systems like medical records (age must be positive integer), financial data (amount must be non-negative), structural engineering (load must not exceed rated capacity), and any system where incorrect data causes safety or compliance failures, not just UI bugs.
A tool for defining the rules your JSON data must follow — types, ranges, lengths, required fields, enums — and generating test data that breaks exactly one rule at a time while satisfying all the others, so you can test each failure mode in isolation.
Chaos testing introduces random, unpredictable problems across a payload. Constraint-violation testing is deterministic and domain-aware — you choose exactly which rule to break, every other field stays valid, and you know precisely which validation path you're exercising.
Required fields, not-null checks, type checks (string, number, boolean, array), numeric min/max ranges, string min/max lengths, enum membership, and regex patterns.
If multiple rules break at once, you can't tell which one caused a given error. Changing one variable at a time means your validation layer's error messages can be checked against a known, single cause — essential for domain-specific systems like medical, financial, or engineering data.
No. The sandbox builds rules and generates violation data entirely client-side in JavaScript — nothing is uploaded to a server.
For broad edge-case testing across an entire JSON payload, use the JSON Chaos Injector. To generate large volumes of realistic test data, use the Correlated JSON Generator. To validate that your base JSON is syntactically correct, use the JSON Validator.
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