Review how an application displays prices, numbers, and dates, then replace manual formatting with Intl APIs that follow language and regional conventions. The skill also checks locale-aware sorting and fallback choices when a requested locale is unavailable.
Use when reviewing utility functions, component props, or template strings that format numbers, prices, or dates to check whether Intl APIs are used correctly.
This skill reviews how prices, numbers, dates, and times are displayed, and helps replace manual formatting with Intl APIs that follow language and regional conventions. It identifies hardcoded currency symbols, digit separators, and date formats, then suggests alternatives using Intl.NumberFormat and Intl.DateTimeFormat. It also checks whether string sorting uses Intl.Collator and reviews fallback settings for cases where the requested locale is unavailable.
Use it when screens serve multiple countries or languages and need consistent treatment of prices and dates according to each locale. It also helps when reviewing shared formatting functions or components and consolidating formatting that has been written manually.
A locale is a setting that specifies language and regional formatting conventions. The material calls for explicitly passing the user's locale instead of relying on the browser default. It also checks for logic that selects a supported fallback when the requested locale cannot be used.
This overview was written by AI (OpenAI Codex) from the public SKILL.md. Check the original below for the exact behavior.
AI rated this skill on four points using only the contents of its SKILL.md. Stars and popularity are not taken into account.
The total counts each point as A = 25, B = 15, C = 5. Rated by AI (OpenAI Codex) as of Oct 23, 2026. Treat it as a guide and read the original before installing.
Review the instructions the agent will receive before you install.
Number and currency formatting rules differ significantly across locales — a value formatted as "$1,234.56" in the US is written "1.234,56 $" in Germany and "¥1,235" in Japan. Hardcoded formatting causes incorrect display for international users and is expensive to maintain manually as you add locales.
Identify all places in this codebase where numbers, currencies, or dates are formatted manually instead of using Intl.NumberFormat or Intl.DateTimeFormat. Also flag locale-sensitive sorting that uses plain string comparison instead of Intl.Collator and any formatter that lacks a fallback locale.
Replace manual number and currency formatting with Intl.NumberFormat and replace manual date formatting with Intl.DateTimeFormat, passing the user locale explicitly. Use Intl.Collator for locale-aware sorting and resolve a supported fallback locale when the requested locale is unavailable.
Explain why locale-aware formatting with Intl APIs is required for international applications, what goes wrong when formatting is hardcoded, and why sorting/searching should also use locale-aware comparison.
Review utility functions and components that render numbers, prices, percentages, or dates. Flag any hardcoded currency symbols, separators, or date format strings, and show Intl-based alternatives.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/i18n/currency-formatting
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