Miller is a command-line tool designed for working with text-formatted data files in multiple formats including CSV, TSV, JSON, and JSON Lines. Whether you're dealing with legacy CSV files or modern JSON data, Miller provides the functionality to manipulate and transform your data efficiently.

The tool serves multiple purposes across different workflows:

Format conversion - Convert between CSV, JSON, TSV and other formats, or pretty-print data horizontally or vertically for easier reading
Data manipulation - Remove unwanted columns, create new calculated fields, and reshape your data structure
Pre and post-processing - Clean and standardize data before loading into databases, or process output from database queries
Interactive exploration - Analyze and understand your data through command-line operations

Miller offers two approaches to data transformation. For simple operations, use compact verbs like sort, head, and cut that work with named fields across multiple lines. For more complex logic, the put verb lets you write programming-language expressions to create calculated fields and apply custom transformations.

The tool is widely used across data analysis, software engineering, DevOps, scientific research, and journalism. At its core, Miller recognizes that most structured data—whether CSV, JSON, or tabular formats—represents lists of key-value pairs, and it leverages this common theme to provide unified handling across different file formats.