Best Online XML Viewer, XML Formatter, XML Editor, Analyser, Beautify-Beautifier, Minify, Tree structure
https://codebeautify.org/xmlviewer

Best JSON Viewer and JSON Beautifier Online
https://codebeautify.org/jsonviewer

Best HTML Formatter and Beautifier
https://codebeautify.org/html-formatter-beautifier

Stack Trace Formatter
https://elmah.io/tools/stack-trace-formatter/

SQL Formatter
https://codebeautify.org/sqlformatter

JSON Diff - Online JSON Compare Diff Finder
https://json-diff.com/

Compare XML files and find Difference Online | TextCompare
https://www.textcompare.org/xml/

Сравнение текстов онлайн
http://text.num2word.ru

Best XML to JSON Converter Online to convert XML to JSON String, URL and File
https://codebeautify.org/xmltojson

HTML to Markdown
https://www.convertsimple.com/convert-html-to-markdown/

Base64
https://base64.guru/

Онлайн-инструменты кодирования и декодирования - DenCode
https://dencode.com

Универсальный декодер
https://2cyr.com/decode

Punycode-конвертер
https://hb.by/punycode-converter.aspx

Экранирование и разэкранирование JSON
https://tools.icoder.uz/json-escape-unescape.php

JSON string escaper
https://www.jsonescaper.com