Regex Match Fixed Length Calculator

Create exact or ranged length expressions with ease. Analyze matches across custom character sets instantly. Download clean reports and inspect results through interactive visuals.

Calculator Input

Length Mode

Exact Length

Minimum Length

Maximum Length

Character Set

Custom Class Content

Anchor Whole String

Case Insensitive

Sample Strings

Add one test string per line. Custom class content should exclude outer brackets.

Example Data Table

Use Case	Character Set	Length Rule	Example Input	Expected Outcome
Product Code	Uppercase letters and digits	Exactly 6	AB12CD	Match
Binary Token	Binary digits	Exactly 8	10101010	Match
Hex Segment	Hexadecimal	4 to 8	1AF9C0	Match
Team Identifier	Custom class A-Z0-9_-	3 to 10	DEV_01	Match
User Alias	Word characters	Exactly 5	john!	No match

Formula Used

Exact length pattern: ^[character_class]{n}$

Range length pattern: ^[character_class]{min,max}$

Character class: Defines allowed symbols, such as [A-Z], \d, or a custom class.

Quantifier: Controls required string length. {6} means exactly six. {4,8} means four through eight.

Anchors: ^ starts matching at the beginning. $ ends matching at the end. They force full-string validation.

Flags: The optional i flag ignores letter case. This is useful when uppercase and lowercase should behave the same.

How to Use This Calculator

Choose whether you need an exact length or a range.
Enter the required length value or the minimum and maximum values.
Select a predefined character set, or enter a custom class.
Choose whether the regex should match the entire string.
Paste sample strings into the textarea, one per line.
Submit the form to generate the regex and validate samples.
Review the result summary, table, and Plotly graph.
Download the evaluation data as CSV or PDF if needed.

Frequently Asked Questions

1. What does fixed length mean in regex?

Fixed length means the string must contain a specific number of allowed characters. A pattern like ^[A-Z]{6}$ accepts only six uppercase letters.

2. When should I use exact length mode?

Use exact mode when every valid string must have the same size. Examples include six-digit OTP codes, eight-bit binary values, or twelve-character inventory identifiers.

3. When is range mode better?

Range mode helps when acceptable inputs vary within limits. Usernames, coupon codes, and short product tags often need minimum and maximum lengths instead of one strict value.

4. Why are anchors important?

Anchors force the entire string to follow the rule. Without them, a valid substring inside a longer invalid line could still return a match.

5. What should I enter in the custom class field?

Enter only the inner class content, such as A-Z0-9_-. The calculator adds the surrounding brackets automatically when it builds the regex.

6. Does this calculator test multiple lines?

Yes. Each line in the sample textarea is checked separately. The result table shows the line number, input value, measured length, and match status.

7. What does the Plotly graph show?

The graph compares sample lengths by line. Green bars represent matches, while red bars show failed validations. This makes pattern behavior easier to review quickly.

8. Can I export validation results?

Yes. The calculator includes CSV and PDF export buttons after a successful calculation. They save the tested sample rows and validation outcomes for reporting.