Format, validate and convert XML, YAML & TOML.
A fast, private toolkit for markup and configuration formats — pretty-print, catch errors, run XPath queries and convert between XML, YAML, TOML and JSON. Everything runs in your browser; your data never leaves the page.
Why MarkupSuite
Pretty-printer
Turn dense XML, YAML or TOML into a clean, indented document with syntax highlighting — or minify XML back to one line.
Validator
Check that your markup is well-formed. Errors report the exact message, line and column so you can fix them in seconds.
Converter
Convert between XML, YAML, TOML and JSON, and run XPath queries against XML — everything through one JSON hub.
Private & offline
Everything runs in your browser. Your files — secrets, tokens and all — never leave the page or touch a server.
Markup formats, made simple
MarkupSuite is a free online toolkit for the markup and configuration formats developers meet every day: XML, YAML and TOML. Pretty-print a dense config into something readable, validate a document to find the one broken tag or misplaced indent, run an XPath query over XML, and convert any of the three to and from JSON. Each format has its own focused tab, so you get a clear answer without juggling a dozen separate sites.
Everything runs client-side in your browser, which makes it fast, private and available offline once loaded. There is nothing to install and no account to create. Because the files you paste never leave the page, it is safe to work with credentials, API keys and internal configuration. And every feature is backed by a plain-language guide that explains the format, its syntax and the mistakes to avoid.
Guides & articles
Plain-language explainers on XML, YAML, TOML and how to work with configuration formats.
XML vs JSON vs YAML vs TOML: How to Choose
Four formats carry most of the world's structured data. Here is how XML, JSON, YAML and TOML differ in verbosity, typing and tooling.
YAML Syntax and Its Most Common Pitfalls
YAML is friendly until whitespace or type-guessing bites you. Learn the core syntax and the handful of traps that cause most YAML errors.
TOML Explained: Config Files Without Surprises
TOML trades YAML's flexibility for strict, obvious rules. Learn its tables, arrays and explicit types — and why Rust and Python chose it.
Frequently asked questions
Is my data sent to a server?+
No. MarkupSuite is a fully client-side application. Formatting, validation and every conversion between XML, YAML, TOML and JSON run in your browser's JavaScript engine, and nothing is transmitted to a remote server. You can safely paste configuration files that contain secrets or personal data; when you close the tab, nothing remains except the clipboard if you clicked Copy.
What is the difference between XML and HTML?+
Both are tag-based markup languages, but they solve different problems. HTML describes how information is presented in a browser and has a fixed set of tags defined by the standard. XML is for storing and transporting structured data — you define your own tags for your domain, such as <invoice> or <customer>. HTML is also forgiving: browsers repair unclosed tags. XML is strict — the first syntax error makes the document not well-formed and unparseable.
Why is indentation so important in YAML?+
In YAML, indentation is part of the syntax — the number of leading spaces defines the hierarchy and nesting of your data. This differs from XML, where tags define the hierarchy, and JSON, where braces and brackets do. You cannot use tab characters, only spaces, and the indentation must be consistent within a block. An inconsistent indent either raises a parse error or, worse, parses the document differently from what you intended, so it pays to run YAML through a formatter before using it.
Can I convert XML to YAML?+
There is no direct XML → YAML button, because the two formats have different structural models, but you can go through JSON as an intermediate step: convert XML → JSON on the XML tab, then paste that JSON into the YAML tab and use JSON → YAML. Keep the limitations in mind: XML attributes have no direct YAML equivalent and usually become object keys (prefixed with @_), while namespaces and processing instructions are lost in the conversion.
What are XML Schema and DTD?+
DTD (Document Type Definition) is an early way to define the allowed structure of an XML document — which elements are permitted, their order and their attributes. XML Schema (XSD) is a more modern and powerful standard, written in XML itself, that adds data types, value constraints, namespaces and type inheritance. MarkupSuite checks that XML is well-formed (syntactically correct) but does not perform full validation against an XSD or DTD; for that, use a dedicated tool such as xmllint.
What is TOML and where is it used?+
TOML (Tom's Obvious, Minimal Language) is a configuration file format created by Tom Preston-Werner for maximum clarity and strictness: each value has an explicit type, and the syntax is unambiguous. It is used by Rust's package manager (Cargo.toml), modern Python projects (pyproject.toml, per PEP 518), the Hugo static-site generator and many other tools. Its main advantage over YAML is the absence of implicit type coercion, which in YAML can produce surprises such as the word NO being read as false.
Do all these formats support comments?+
Yes. XML uses <!-- comment --> (block style, can span multiple lines); YAML and TOML both use # comment for single-line comments from the hash to the end of the line. The one popular format that does not support comments is JSON — that omission is a major reason YAML and TOML became so common for configuration files. Extensions like JSON5 and JSONC add comments to JSON, but they never became an official standard.
Are there limits on file size?+
MarkupSuite runs entirely in the browser and never uploads data, so the practical limit is your device's memory. Files up to a couple of megabytes are handled without noticeable delay on a modern machine; very large files (tens of megabytes) may process slowly or briefly freeze the tab. For huge documents — database dumps and the like — reach for command-line tools such as xmllint, yq or dasel instead.