Formatters

Formatters are software tools or components that convert data from one representation into another in order to improve readability, consistency, or presentation. They typically preserve the underlying data value while altering its appearance, layout, or syntax to meet a target style or locale.

Formatters can be classified by the kind of data they handle. Text formatters adjust line width, indentation, wrapping, and punctuation to produce clean, readable text. Data formatters convert numbers, dates, times, currencies, and units into locale-aware strings. Code formatters enforce consistent style in source code, aligning tokens, spaces, and line breaks without changing the program’s behavior. Report and document formatters generate formats such as HTML, PDF, or XML from data sources, often applying templates or styles.

Common features include support for locale awareness, configurable format patterns or templates, and idempotence (reformatting should not produce further changes if already formatted). They are often integrated into editors, build pipelines, or data processing workflows, running as a pre-commit check, a compile-time step, or a runtime formatter for display.

In practice, formatters aim to reduce cognitive load and noise in diffs, logs, and reports, while enabling consistent presentation across teams. Examples include language code formatters (Prettier, clang-format), date/number formatters in standard libraries (DateTimeFormatter, NumberFormat), and pretty-printers or data pretty print utilities. See also: pretty printer, formatter, localization.