TOPCAT

TOPCAT is an interactive graphical viewer and editor for tabular data, designed primarily for astronomers but usable with any table‑based dataset. It supports a range of formats—including FITS, VOTable, CDF, CSV, ASCII, and Parquet—and can be extended to additional types. The application excels at exploring large tables with millions of rows and many columns, offering cell‑level browsing, metadata inspection, and flexible 1‑D to multi‑dimensional visualisation.

Users can define new columns, select row subsets, and perform calculations through a Java‑based expression language. Editing capabilities allow modification of both data and metadata, with export to many output formats. The tool includes global variables with interactive sliders, additional axis scaling options (asinh, symlog), and configurable CSV delimiters and type inference.

TOPCAT runs as a stand‑alone Java program on macOS, Linux, and Windows, requiring no network connection, yet it integrates with Virtual Observatory standards for interoperability with other services and tools. It is released under the GNU GPL, with some LGPL components.