TOML to JSON

What it does

TOML (Tom's Obvious Minimal Language) was created by Tom Preston-Werner in 2013 specifically to address frustrations with YAML's ambiguity (significant whitespace gotchas) and JSON's verbosity (no comments, awkward for human-edited config files). It's become the dominant config format for several modern toolchains: Rust uses Cargo.toml for package manifests, Python adopted pyproject.toml as the standard build-system config (PEP 518/621/660 making it the lingua franca for setuptools, poetry, flit, hatch, pdm), and Go, Hugo, and many other tools use TOML for configuration.

Converting TOML to JSON is useful when you need to feed config data into a tool that only accepts JSON (most JS frontends, many Node.js libraries, generic schema validators that target JSON Schema), pipe TOML through jq for inspection or transformation, or serialize TOML data over an API that standardizes on JSON. The conversion is straightforward because TOML's data model is essentially a typed subset of JSON: tables become objects, arrays become arrays, strings/integers/floats/booleans map 1:1, dates and times become ISO 8601 strings.

Caveats and gotchas: TOML supports comments (# at start of line); JSON doesn't — comments are silently dropped during conversion. TOML has explicit datetime types (offset, local, date, time); these become JSON strings since JSON has no datetime type. TOML supports inline tables {...}and arrays of tables ([[name]]); both translate naturally to nested JSON objects and arrays of objects. The conversion is one-way safe (TOML always converts to JSON cleanly); going JSON→TOML can fail if the JSON has features TOML doesn't (deeply nested mixed types, null values — TOML has no null).

How to use it

1. Paste your TOML content (Cargo.toml, pyproject.toml, or any TOML config) into the input.
2. Click Convert — the tool parses TOML and emits equivalent JSON.
3. Copy the JSON output, with optional pretty-print indentation (2 or 4 spaces).
4. Use the JSON in tools that accept JSON-only config or pipe through jq for further transformation.

When to use this tool

• Feeding Rust Cargo.toml metadata into a JS-based dependency analyzer.
• Converting pyproject.toml for use with tools that consume JSON config (some CI tools, schema validators).
• Quick inspection of unfamiliar TOML files — JSON is more compactly readable in many viewers.
• Migrating config from TOML to JSON-based formats (some legacy tools).
• Building tooling that reads TOML configs and emits JSON for downstream consumption.

When not to use it

• When you need round-tripping with comments preserved — comments are lost.
• When the destination tool natively reads TOML (Cargo, Python build tools, Hugo) — no conversion needed.
• Production config pipelines where you need a real TOML parser library (smol-toml, @iarna/toml) with proper error handling, not browser-based one-off conversion.
• Validating TOML against a schema — convert to JSON first, then run JSON Schema validation (no native TOML schema standard exists).

Common use cases

• Verifying a number or output before passing it on
• Quick conversion during a typical workday
• Pre-decision sanity-check on inputs and outputs
• Educational use — demonstrating the underlying concept