application.properties ↔ application.yml Converter

Paste a Spring Boot application.properties file to convert it to application.yml — or paste YAML to get properties back. It handles lists, profiles, multi-document files, and comments, and when a file won’t parse it tells you why, where, and offers a one-click fix. Everything runs in your browser; nothing is uploaded or stored.

How this converter is different

• It repairs broken files, not just flags them. Most converters fail silently or throw a stack trace on bad input. This one gives a plain-English message and a one-click fix button — “Add the colon”, “Close the quote”, “Use spaces instead of a tab”.
• It catches the mistakes tools usually miss. A key run into its value (server.port8080), a double dot (spring..name), a first list element missing its [0] — each gets the right fix, not a blind one.
• It finds invisible characters. Curly quotes, non-breaking spaces and zero-width marks from pasting out of a browser, Word or Confluence — the single most baffling class of YAML bug — are detected and cleaned on request.
• It knows Spring’s multi-document format. YAML documents split by --- become #--- blocks in properties, exactly as Spring Boot 2.4+ expects.
• It keeps your comments and carries them across, attached to the key they describe.
• It’s 100% private. Everything runs in your browser; your config never leaves your machine.

What this tool does

• Two-way conversion — .properties to .yml and back.
• Lists — key[0]=value becomes a YAML - value list, and vice versa.
• Lists of objects — indexed keys like clients[0].name convert to a proper list of maps.
• Profiles & multi-document files — --- in YAML maps to #--- in properties.
• Comments preserved — carried across and attached to the following key.
• Plain-English errors with one-click repair — missing colon, tab indentation, unclosed quote or bracket, trailing backslash, double dot, and more.
• Options — 2- or 4-space indent, and original or sorted key order.

Should I use .properties or .yml in Spring Boot?

Both are read the same way by Spring Boot, so it’s a style choice. YAML is more compact for deeply nested keys and lists and is the common choice for new projects; properties is flatter and easier to override per line. Many teams standardise on YAML and use this tool to convert an existing application.properties in one step.

Common conversion errors — and what they mean

“This line is indented with a tab”

YAML does not allow tabs for indentation — only spaces. This is the most common reason a YAML file won’t parse. The tool detects it and can convert every tab to spaces in one click.

“Not a key: value pair” (missing colon)

YAML needs a colon and a space after each key, e.g. port: 8080, not port 8080. The tool inserts the colon for you.

Key run into its value, e.g. server.port8080

A missing = between a key and its value. The tool recognises the key server.port and the value 8080 and inserts the = in the right place.

Double dot in a key, e.g. spring..name

Two dots in a row leave an empty level in the key. The tool flags it and removes the extra dot, producing spring.name.

List item missing its first index

If servers=a is followed by servers[1]=b, the first line most likely needs a [0]. The tool spots the mismatch and adds it.

Invisible characters from copy-paste

Curly quotes (“ ”), non-breaking spaces and zero-width marks — usually from pasting out of a browser, Word or Confluence — look correct but break parsing. The tool detects them and cleans them on request.

Is my data safe?

Yes. This tool is 100% client-side — the configuration you paste never leaves your browser. There is no server call, no logging, and nothing is stored.

Frequently asked questions

Does it handle multiple Spring profiles in one file?

Yes. A multi-document YAML file separated by --- converts to #----separated blocks in properties, which is the format Spring Boot 2.4 and later expect for profile-specific config.

Are my comments kept?

Yes. Comments are carried across in both directions and attached to the key that follows them.

Does this work offline?

Once the page has loaded, conversion runs entirely in your browser, so it keeps working without a connection.

Is there a size limit?

There’s no hard limit, but very large files may convert more slowly because everything runs in the browser.