Historical Currency Value Converter

WHAT IT DOES

This userscript scans every page you visit for monetary amounts written with currency symbols ($, €, £, ¥, ₽, etc.) or three-letter currency codes (USD, EUR, GBP, JPY, etc.). For each detected value, it looks nearby for a date reference—anything from "January 15, 2020" to "15/01/2020" or "2020-01-15". It then fetches the exact historical exchange rate for that specific date from a free public API and converts the amount to your preferred base currency. The original value remains visible, with the converted amount appended in parentheses right next to it. If no date is found, it uses the most recent available rate.

WHERE IT RUNS

The script operates on every website you visit—news articles, financial reports, e-commerce listings, forums, blogs, or any page containing monetary references. It runs entirely within your browser, reading only the current page's text content. It does not track your browsing history, access other tabs, or send your data anywhere except for the exchange rate API calls required for conversion.

HOW TO USE

After installation, open the panel by clicking the tool's icon in the BotGentz sidebar. Select your base currency from the dropdown (USD, EUR, GBP, etc.) and toggle whether you want to use historical dates when detected—this is on by default. Click "Convert values on page" and watch as every monetary amount on the page gets annotated with its converted value. The panel shows a progress counter and reports how many values were converted. If you want to revert to the original page, click "Reset page" to reload it without any changes.

THE TECHNICAL MECHANISM

Unlike simple currency converters that only apply today's exchange rate, this script performs date-aware conversion by constructing API queries with a 'date' parameter. When it finds a date adjacent to a monetary amount, it extracts the year, month, and day using a cascade of regex patterns that match ISO, US, European, and named-month date formats. The date is then passed to the exchangerate.host API endpoint, which returns the exact mid-market rate for that calendar day from its historical database. This provides accurate inflation-adjusted comparisons rather than anachronistic present-day conversions. The script also batches API requests to respect rate limits, processing up to four conversions concurrently with 300-millisecond delays between batches.

THE PANEL

The panel is draggable anywhere on the screen and remembers its position between sessions. It can be collapsed to a small floating bubble to minimise distraction, and expanded again with a single click. The panel's width can be adjusted, and pressing the Escape key closes it instantly. All settings—your chosen base currency and the historical toggle state—are persisted locally using GM_setValue, so your preferences remain intact across page reloads and browser restarts.

PLEASE NOTE

This userscript requires the free BotGentz extension to function. It relies on the exchangerate.host API, which is a free service with usage limits; if you perform many conversions in rapid succession, you may encounter temporary rate limiting. The script only modifies text nodes on the page and does not interact with password fields, hidden inputs, or file uploads. Websites change their structure over time, so the script's ability to detect currency values depends on how content is presented—it works best with plain text and may not detect values inside complex dynamic widgets or canvas-rendered content. No data from your browsing is stored or transmitted beyond the explicit API requests for exchange rates.