What happens to `app.hosts[0]`?

It becomes a list, since this page was written. Those indexed keys are how Spring writes a sequence into a flat file, and this site’s YAML-to-properties tool writes them that way too — but reading them gave you literal keys named `hosts[0]` and `hosts[1]`, so the tool did not recognise its own output. A run of indexes starting at 0 with no gap now becomes a YAML sequence; anything less regular stays literal, because guessing at a position would move a value.

Why did `007` come out quoted?

To keep it a string. Values are typed the way this site types CSV — `8080` is a number, `true` is a boolean — but `007` is an identifier whose zeros matter, so it stays text. Quoting also protects what YAML 1.1 readers would misread: `y`, `on` and `NO` are strings in your file and booleans to PyYAML, so they are written with quotes and stay themselves.

Properties to YAML — Spring Boot Ready

Turn a Java .properties file into YAML. Dotted keys nest and indexed keys become lists, giving you an application.yml you can commit as is.

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Indentation

Swap: YAML → Properties

Properties input

YAML output

What this tool does

A .properties file becomes YAML, with the dots turned into structure.

# service
app.name=Demo
app.port=8080
app.debug=true

app:
  name: Demo
  port: 8080
  debug: true

= and : both separate a key from its value, comment lines start with # or !, and a line ending in a backslash continues on the next one. The escapes a .properties file uses — \:, \=, \n, \uXXXX — are decoded, so caf\u00e9 arrives as café.

Indexed keys become lists

app.hosts[0]=alpha
app.hosts[1]=beta

app:
  hosts:
    - alpha
    - beta

That is how Spring writes a list into a file that has no lists, and it is what this site’s YAML-to-properties converter produces. Reading it, though, gave you two literal keys called hosts[0] and hosts[1]: the tool did not recognise its own output, and a round trip lost the sequence. Indexes now become a sequence when they run from 0 with no gap. A gap, a repeat, or a plain hosts next to them leaves the keys exactly as they were — moving a value to fill a hole would be inventing an order.

A repeated key is refused

app.port=8080
app.port=3000

Duplicate key "app.port": it already has a different value

Properties.load keeps the last assignment without a word, so the first value vanished. The YAML-to-properties direction already refused to write two keys that flatten to the same name; accepting them here in silence was the same hole seen from the other side. Two identical lines still pass, because repeating yourself is not the admission of anything.

What the values become

Numbers and booleans are typed, as they are in the CSV tools: 8080 is a number, true is a boolean.
007 stays a string. So does 1e3, and anything else whose text carries more than its value.
Ambiguous scalars are quoted. y, on and NO are strings to a YAML 1.2 reader and booleans to PyYAML, which reads YAML 1.1. Quoting exactly those keeps both readers in agreement.
An empty value is an empty string, not a null: the file says the key is there with nothing in it, and that is what the YAML says too.

Private by design

Everything runs locally in your browser with JavaScript. Your data is never uploaded, which makes the tool safe for sensitive content, and it keeps working offline.

Frequently asked questions

What happens to `app.hosts[0]`?: It becomes a list, since this page was written. Those indexed keys are how Spring writes a sequence into a flat file, and this site’s YAML-to-properties tool writes them that way too — but reading them gave you literal keys named `hosts[0]` and `hosts[1]`, so the tool did not recognise its own output. A run of indexes starting at 0 with no gap now becomes a YAML sequence; anything less regular stays literal, because guessing at a position would move a value.
Why is a repeated key refused?: `Properties.load` keeps the last one and says nothing, so the first value simply disappeared. The other direction already refused to write two keys that flatten to the same name; reading them in silence was the other half of the same hole. Two identical lines are not the admission of anything and still pass.
Why did `007` come out quoted?: To keep it a string. Values are typed the way this site types CSV — `8080` is a number, `true` is a boolean — but `007` is an identifier whose zeros matter, so it stays text. Quoting also protects what YAML 1.1 readers would misread: `y`, `on` and `NO` are strings in your file and booleans to PyYAML, so they are written with quotes and stay themselves.