About
Toolbox is a collection of small web tools. The English edition has three tools for now: a JSON formatter, a text compare tool and a ladder game. Each page puts the tool first, and the explanation and examples come after it.
Except for the Korean building register lookup, what you enter is processed in this browser and is not sent to a server
Why we built it
Many small web tools give you an answer but not the reason behind it. When the result looks wrong, you cannot tell whether the tool made a mistake or you typed something differently. Toolbox tries to show how each result was reached. Under every tool you will find how it works, worked examples that we ran through the tool itself, and the edge cases where it behaves in a way you might not expect.
Who runs it
Toolbox is built and run by Fillus. Fillus also fixes the tools and answers the emails sent to this site.
Most of the site is in Korean. The Korean edition has calculators for Korean tax, loans, savings and severance pay, and lookups that use Korean public data. The English edition has three tools that work the same way in any country: a JSON formatter, a text compare tool and a ladder game.
How to check a calculation
The explanations under each tool are drafted by Fillus with AI and checked in two ways before they go live.
- Every worked example in the text is run again through the tool on this site, and the numbers in the text must match the result on the screen.
- Where a tool follows a published standard, the text is checked against the original. The JSON formatter, for example, follows the JSON standard, RFC 8259.
Both checks are done by AI. When we change how a tool works, we run a fixed set of examples again to make sure that results which were right before are still right.
You can check a result yourself, too. Each page explains the method step by step, so you can redo a small example by hand and compare.
Found a mistake?
There may still be mistakes. If a tool gives a wrong result, or the explanation does not match how the tool behaves, please tell us by email from the contact page. We will look into it, fix it, and change the “Updated” date on that page.
Ads and cost
All tools are free and need no sign-up. The site is paid for by ads, so you may see ads on its pages. Ads are labeled and kept apart from the tools and their results. Advertisers have no say in how a tool works or what its explanation says.
For reference
The results and explanations are for general reference. They are not professional advice. Before you rely on a result for something important, check it against the original source or ask someone qualified.
Who runs this site
- Operator
- Fillus (필어스)
- Representative
- Park Kiwan (박기완)
- toolbox@gofillus.com