Random String Generator

Placeholder Strings of 1 to 1000 Characters

Create ASCII character strings for test fixtures, mock identifiers and format experiments. Choose 1 to 1000 source characters and a count of 1, 5, 10, 20 or 50. Repeated characters and duplicate strings are possible. This tool does not implement a token service, JWT signing or encryption-key management. Use it to fill form and length tests with placeholder strings, to compare grouped and unformatted strings in a prototype, to try letter-only or numeric strings against a field in a test environment, or to see how case conversion affects output.

Choosing Character Set, Length and Format

1. Choose Mixed Characters, Alphanumeric, Letters Only or Numbers Only.
2. Enter a whole-number length, then choose count, case and exclusions.
3. Choose formatting and click Generate Strings. Settings apply to the next batch.
4. Copy a named result or Copy All for one formatted string per line. If Copy fails, select the text manually.

How the Randomness and the Entropy Estimate Work

Web Crypto supplies 32-bit values. Rejection sampling selects source characters without modulo bias. Exclusions remove both listed source characters and characters whose case conversion would produce 0, O, l, 1 or I. Title Case uppercases the first source position only.

The rounded Shannon estimate uses each output character's probability after filtering and case conversion, separately for the first position in Title Case. Case conversion can merge outcomes with unequal probabilities. Separators add no randomness. The estimate describes the current settings, not an existing result or a measured attack cost.

Eight Characters, Four Formats

For an eight-character demonstration string abcdefgh, formatting changes only the separators. This example illustrates formatting; it is not a secret to reuse.

Length, Separators and URL Safety

Length counts source characters, not added separators. A blank field, fractional length or value outside 1 to 1000 produces an error and clears the old batch. If the random source fails, no partial batch or weaker fallback is returned. Changing settings clears Copy feedback but preserves the displayed batch until generation or Clear.

Alphanumeric source characters do not make every formatted result URL-safe: Space adds spaces, and Mixed can include reserved punctuation. There is no uniqueness guarantee or required-character-category guarantee. A numeric string is not a complete one-time-password system.

Choose No format when the target expects an uninterrupted string, and follow that target's own requirements. For production authentication, use the relevant application or password-manager workflow. MDN explains Web Crypto and recommends a dedicated key-generation API for cryptographic keys.