How do I define column widths?

Enter a comma-separated list matching your record layout — e.g. 5,10,20,8 for four fields. The viewer colours each field alternately so you can distinguish them easily.

What is the difference between fixed-length and CSV?

CSV uses delimiters (commas, tabs) between variable-length fields. Fixed-length files use no delimiters — position and width identify fields. Faster for batch processing but requires a layout specification to read.

Is the file uploaded to a server?

No. All parsing happens in your browser. Your file contents are never transmitted to any server.

Fixed-Length File Viewer — Parse & Visualize Fixed-Width Files

☁ Upload File

Or Paste File Content Here Paste your fixed-length file content here (updates automatically)

What Is a Fixed-Length File Viewer?

A fixed-length file (also called a fixed-width or flat file) is a text format where every field occupies a fixed number of characters — no commas, no delimiters, just position and length. These files are ubiquitous in legacy mainframe systems, COBOL batch jobs, banking transaction exports, and government data exchanges. Our browser-based viewer lets you paste or upload such a file and instantly see each column highlighted by width, turning an unreadable wall of characters into a structured, colour-coded table.

Key Features

Interactive grid view: Each character in its own cell with exact positioning
Custom column widths: Define any field layout as a comma-separated list (e.g. 10,5,20,8)
Row & column selection: Click headers to select entire rows or columns
Drag selection: Click and drag to highlight rectangular regions
Whitespace visualisation: Empty spaces marked with dots (·)
File upload: Upload .txt, .dat, or .csv files up to 10 MB

How to Use the Fixed-Length Viewer

Paste your fixed-length text or upload a .txt file
Enter the field widths as a comma-separated list matching your record layout (e.g. 5,10,8,30,12)
The viewer splits each line into labelled, colour-coded columns
Click or drag cells to select specific fields for inspection

Common Use Cases

Mainframe data migration: Inspect extract files from IBM z/OS or AS/400 systems before importing
COBOL batch output: Validate record layouts from COBOL report programs
Banking & finance: Parse ACH, SWIFT, or bank statement flat files
Government data exchanges: View tax, benefits, or census fixed-width records
Legacy ETL debugging: Identify off-by-one errors in field widths during data transformation

Fixed-Length vs CSV

CSV uses delimiters (commas, tabs) between variable-length fields. Fixed-length files use no delimiters — fields are identified purely by character position and width. This makes them faster for batch processing but harder to read without a layout specification.

Frequently Asked Questions

What is a fixed-length file?: A file where each field occupies a fixed number of characters, with no delimiters between fields. Fields shorter than their allotted width are padded with spaces. Standard in COBOL, mainframe, and legacy banking systems.
How do I define column widths?: Enter a comma-separated list matching your record layout — e.g. 5,10,20,8 for four fields. The viewer colours each field alternately so you can distinguish them easily.
What is the difference between fixed-length and CSV?: CSV uses delimiters (commas, tabs) between variable-length fields. Fixed-length files use no delimiters — position and width identify fields. Faster for batch processing but requires a layout specification to read.
Is the file uploaded to a server?: No. All parsing happens in your browser. Your file contents are never transmitted to any server.

Privacy & Security

File contents are processed entirely in your browser. Nothing is uploaded to our servers. You can safely inspect files containing confidential banking, payroll, or personal data.