How does the parser know when a block ends?

By indentation width: once a line's leading-space count drops back to or below the level where the current block started, that block is finished and the parser returns to the level above. Lines at a deeper indent than expected mid-block are reported as an indentation error with the exact line number.

What counts as a valid inline array element?

The literals true, false, and null, a number, a double-quoted string (with \\, \", and \n unescaped), an empty inline object {}, or another nested [...] array, matching exactly what jsonToCson can produce. Commas inside quoted strings are handled correctly and won't split an element early.

What does an empty document parse to?

An empty or whitespace-only input parses successfully to {}, treating the empty CSON document as the empty-object case rather than as an error, which mirrors how JSON to CSON renders an empty object as empty output.

What happens on a line that isn't valid CSON, like plain prose?

The parser reports the exact line number and a message explaining it expected a "key:" or "key: value" line there, rather than silently skipping or guessing at the intended structure.

CSON to JSON Converter - Convert CoffeeScript Object Notation Online

Overview

Introduction

CSON's indentation-based syntax is easy to hand-write but not something most JavaScript/TypeScript tooling understands natively.

This tool parses that CSON subset directly into JSON, so a CoffeeScript-style config file can be inspected, validated, or fed into any JSON-consuming tool.

What Is CSON to JSON Converter?

A line-based parser (modeled after a minimal YAML block parser) that reads 2-space indented key: blocks and key: value leaf lines and reconstructs the equivalent nested JSON object.

It understands the same subset jsonToCson produces: bare or double-quoted keys, block-nested objects, and inline [...] arrays of literals, numbers, strings, and nested arrays.

How CSON to JSON Converter Works

The input is split into lines, blank lines are skipped, and each remaining line's leading-space count becomes its indentation width. A recursive block parser consumes a contiguous run of lines at the same indentation, treating a bare key: line (nothing after the colon) as the start of a nested block formed from the following, deeper-indented lines.

A key: value line's value is parsed by a small recursive value parser that handles literals, numbers, quoted strings, and inline arrays, splitting array contents on top-level commas while correctly skipping over commas inside quoted strings.

When To Use CSON to JSON Converter

Use it to read a CoffeeScript project's CSON config into a JSON-based build script or validation tool.

It's also handy for quickly checking a hand-written CSON snippet's actual structure by seeing it as familiar JSON.

Often used alongside JSON to CSON Converter, YAML to JSON Converter and JSON Formatter & Beautifier.

Features

Advantages

Reports a specific line number for malformed input, whether it's bad indentation or an unparseable value.
Handles quoted strings containing commas or brackets correctly when splitting inline array elements.
Treats an empty document as a valid empty object rather than forcing an artificial error.

Limitations

Doesn't support CoffeeScript's full executable object-literal syntax, dash-prefixed list arrays, comments, or multi-line strings, only the plain-data subset this site's JSON to CSON converter produces.
A line with inconsistent indentation (deeper than expected without a preceding bare key: line, or a level that doesn't match any enclosing block) is reported as an error rather than guessed at.

Examples

Nested block and inline array

Input

name: "api"
port: 3000
debug: false
tags: ["web", "api"]
db:
  host: "localhost"

Output

{
  "name": "api",
  "port": 3000,
  "debug": false,
  "tags": [
    "web",
    "api"
  ],
  "db": {
    "host": "localhost"
  }
}

Each leaf key: value line becomes a JSON property, and the db: block becomes a nested object.

A line with no key/value structure

Input

this is not valid cson

Output

Line 1: expected a "key:" or "key: value" line.

The line doesn't match either the bare-key or quoted-key pattern, so parsing fails at that exact line.

Best Practices & Notes

Best Practices

Use exactly 2 spaces per indentation level; mixing tabs and spaces or using inconsistent widths is the most common source of indentation errors.
Check the reported line number against the source when parsing fails, most failures come from a stray unindented line or a malformed inline array.
Pair with JSON to CSON to round-trip a conversion and confirm it comes back the way you expect.

Developer Notes

The block parser is written as a small recursive-descent function keyed entirely on line indentation rather than building a token stream first: each call consumes a contiguous run of same-indent lines and recurses into any deeper-indented run it finds under a bare key: line, which keeps the implementation close to a one-pass reader while still handling arbitrarily deep nesting correctly.

CSON to JSON Converter Use Cases

Reading a hand-written CSON config file's structure from a JavaScript/TypeScript build script
Converting a CoffeeScript project's CSON config into JSON for tooling that only accepts JSON
Validating that a CSON snippet is well-formed before committing it to a project

Common Mistakes

Mixing indentation widths across sibling lines, which the parser reports as an inconsistent-indentation error rather than silently normalizing.
Expecting comments (# ...) to be ignored; this parser doesn't strip comments, so a comment line will fail to parse as a key: line.
Assuming dash-prefixed list arrays parse; only inline [...] arrays are supported.

Tips

If parsing fails, check the reported line first, most issues are either a missing colon or a mismatched indent width.
Use JSON to CSON to generate valid input for this converter if you're unsure of the exact grammar it expects.

CSON to JSON Converter