Regex Substitution & Expansion Estimator

Estimate string replacement length deltas, payload expansion percentages, and token count modifications for regex substitutions.

  • 100% free
  • Private in browser
  • No signup
  • No watermarks
Net Output Length Change (+/- chars)
48
Final Transformed Text Length
548
Length Expansion / Contraction (%)
9.6
Total Characters Replaced
48

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About Regex Substitution & Expansion Estimator

Estimate string replacement length deltas, payload expansion percentages, and token count modifications for regex substitutions. Enter Sample Text Length, Pattern Matches Count and Average Matched Token Length and the tool works out Net Output Length Change, Final Transformed Text Length and Length Expansion / Contraction straight away. Everything runs in your browser, so your data never leaves your device.

How to use Regex Substitution & Expansion Estimator

  1. Enter Sample Text Length, Pattern Matches Count and Average Matched Token Length.
  2. Adjust the remaining options (Average Replacement Length) to match your case.
  3. Read Net Output Length Change, Final Transformed Text Length and Length Expansion / Contraction in the results panel — copy or download what you need.

Key features

  • Shows Net Output Length Change (+/- chars)
  • Shows Final Transformed Text Length
  • Shows Length Expansion / Contraction (%)
  • 4 adjustable inputs, results update as you type
  • No signup, no limits

Frequently asked questions

Is this calculation free and private?
Yes, 100% of calculations execute locally in your web browser. No inputs or personal data are stored or transmitted.
What does the Regex Substitution & Expansion Estimator give me?
It works out Net Output Length Change, Final Transformed Text Length, Length Expansion / Contraction and Total Characters Replaced, updating live as you change the inputs.
What do I need to enter?
Just Sample Text Length, Pattern Matches Count, Average Matched Token Length and Average Replacement Length. Every field has a sensible default you can start from.
Is my data uploaded anywhere?
No. The calculation runs in your browser with JavaScript — nothing you type is sent to a server or stored.
Does it work on a phone?
Yes. The layout adapts to small screens and needs no app or signup.
Regex Substitution & Expansion Estimator | TheToolss