List Combiner

Why You Need a List Combiner

You have two lists. Maybe usernames in one file and passwords in another. Or product names and their prices. Or email prefixes and domain names. You need to combine them somehow—either stacked together, alternating, or paired up.

Spreadsheet software can do this for small datasets. But when you're dealing with lists containing millions of items, Excel crashes or takes forever. Command-line tools work but require scripting knowledge most people don't have.

We built this list combiner to handle massive files efficiently, with a simple interface that anyone can use. Everything runs in your browser—your data never leaves your device.

Three Ways to Combine Lists

Merge Mode (Concatenate)

The simplest approach: put all of List A first, then all of List B after it.

• Input A: [apple, banana, cherry]
• Input B: [dog, elephant, fox]
• Output: [apple, banana, cherry, dog, elephant, fox]

Use merge when you want to consolidate multiple files into one, or when the order within each list matters more than mixing them.

Interleave Mode (Alternate)

Alternates between lists, taking one item from each in turn.

• Input A: [apple, banana, cherry]
• Input B: [dog, elephant, fox]
• Output: [apple, dog, banana, elephant, cherry, fox]

Use interleave when you want items distributed evenly—useful for load balancing, A/B testing lists, or creating varied sequences.

Combination Mode (Pair All)

Creates every possible A:B pair from both lists.

• Input A: [user1, user2]
• Input B: [pass1, pass2, pass3]
• Output: [user1:pass1, user1:pass2, user1:pass3, user2:pass1, user2:pass2, user2:pass3]

Practical Use Cases

Creating Credential Lists

Combine a username list with a password list using combination mode. Set the separator to ":" for standard credential format. Limit combinations if your lists are large.

Email Generation

Combine name prefixes with domain names. List A: [john, jane, bob]. List B: [@gmail.com, @yahoo.com]. Get all possible email combinations.

Data Consolidation

Merge multiple export files into one. Use merge mode to stack data from different sources, then run through our duplicate removal tool to clean up.

Test Data Generation

Generate test datasets by combining first names, last names, and email domains. Chain multiple combination operations for complex data structures.

Options Explained

• Separator: Character between A and B in combination mode (default: colon)
• Max Combinations: Limit output size to prevent memory issues with large lists
• Remove Duplicates: Automatically deduplicate the final output
• Randomize: Shuffle the result using Fisher-Yates algorithm
• Trim Lines: Remove leading/trailing whitespace from each line
• Skip Empty Lines: Ignore blank lines in input

Performance and Privacy

Everything processes in your browser using chunked file reading. We handle large files in 4MB chunks to prevent memory issues. Your data never uploads to any server.

For combination mode with very large lists, consider the math: A×B pairs can explode quickly. Use the Max Combinations limit to control output size.