randarium
Test Data

Fuzz Values Generator

Create collections of boundary values, null/undefined literals, NaN/Infinity, deeply nested objects, and huge arrays for negative testing and fuzzing. Output is serialized JSON strings suitable for validation and parser testing.

Also known as: edge case generator · boundary test data

seeded · synthetic data

Presets

Output

No output yet — set your options and hit .
About this tool, tips & examples

What it does

The Fuzz Values Generator produces the values that crash naive code: boundary integers (0, −1, 2³¹−1, 2⁵³…), null/undefined literals, NaN and Infinity, deeply nested objects, and huge arrays — serialized as JSON strings ready to throw at parsers and validators. Generate up to 1,000 values per run, seeded so the case that broke your code is pinned forever.

Common use cases

  • Negative testing — table-driven tests over inputs your API should reject gracefully instead of 500-ing.
  • Parser hardening — deep nesting and huge arrays expose recursion limits, quadratic paths, and memory blowups.
  • Validation coverage — does your schema actually catch NaN? String "null" vs literal null? Off-by-one at integer boundaries?
  • Error-handling QA — verify that failures produce useful messages, not stack traces.

Settings

  • Value type — boundary values, null/undefined, nested objects, huge arrays, or a mix (presets for each).
  • How many — 1 to 1,000 values per run, exportable as text, JSON, or CSV.
  • Seed — the same seed and settings reproduce the identical set — keep the seed in the bug report.

Privacy note

Values are generated locally in your browser and never uploaded. They are synthetic test payloads — deliberately awkward, entirely benign, and never real data.

FAQ

Why do boundary integers matter? Because that’s where representations break: 2³¹ overflows 32-bit ints, 2⁵³ exceeds JavaScript’s safe-integer range, and −1 slips past unsigned assumptions. Bugs cluster at edges; so should tests.

Is this real fuzzing? It’s the fixture side of it — curated hostile values for deterministic tests. Coverage-guided fuzzers (AFL, libFuzzer, fast-check) explore further; these values make excellent seed corpora for them.

Hostile strings rather than structures? That’s the Edge Case Strings generator — Unicode, RTL, and injection-shaped text. Use both for full input coverage.