[yisonlee888]

Add a single README entry under ## Productivity and Workflow Tools.

ToolStack is a free online toolbox of 122 utilities (JSON, Base64, regex, JWT, HTTP status, color, text, image, PDF, unit conversion) that run entirely client-side in the browser. Files are never uploaded to a server and no signup is required. It fits this list because it is a daily workflow tool for developers: each one opens as a single page, with no install and no account.

The entry uses the [Name](URL) - Description. format, the description ends with a period, and the link is a canonical HTTPS URL without tracking parameters.

Type of change

• Add a new resource
• Update an existing resource
• Fix formatting/typos
• Improve categorization

Checklist

• I have read contributing.md.
• My change is specifically relevant to developer essentials.
• I used the format [Name](URL) - Description. for list entries.
• I checked for duplicate entries.
• Descriptions are concise, objective, and end with a period.
• I verified links are valid and not broken.
• I used canonical HTTPS URLs without shorteners or tracking parameters.
• I disclosed any affiliation with the added/updated resource.
• This pull request contains a single logical change.

Additional context

Disclosure: I maintain ToolStack, so this is a self-submission. The diff is one added line (1 addition, 0 deletions); there are two commits because I reworded the description so it starts with a capital letter.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[nimrodkra]

Thanks for the submission. We prefer to list focused tools over large multi-tool collections, so we'll pass on this one.