How do I convert a TOML file to JSON?

Open your TOML file, copy its contents, and paste them into the input panel with the direction set to TOML → JSON. The JSON appears instantly on the right. Pick your indentation (2 spaces, 4 spaces, tab, or minified) and use Copy or Download to save a .json file. Everything runs in your browser — the file is never uploaded.

Can I convert JSON back to TOML?

Yes. Switch the toggle to JSON → TOML. The JSON root must be an object (TOML's top level is a table), so a bare array or string is rejected with a clear message. Arrays of objects become TOML arrays of tables ([[name]]), nested objects become [table] sections, and the result is downloadable as a .toml file.

What happens to TOML dates when converting to JSON?

JSON has no date type, so TOML offset date-times, local date-times, local dates, and local times all become ISO-8601 strings (for example 2026-06-24T10:30:00Z becomes "2026-06-24T10:30:00.000Z"). The type-mapping notes panel reports exactly how many and which kinds were converted, and the round-trip check flags the result as "converted with notes".

Why can't JSON null be converted to TOML?

The TOML v1.0.0 specification has no null type — there is no valid way to write "this key has no value". Rather than invent a sentinel, this converter omits any key whose JSON value is null and tells you how many were dropped in the notes panel. A null inside an array is a hard error, because a TOML array cannot contain one.

What's the difference between a TOML table and an array of tables?

A table is a single [section] that maps to one JSON object. An array of tables uses double brackets ([[section]]) and maps to a JSON array of objects — each [[section]] block is one element. So JSON {"users":[{"name":"a"},{"name":"b"}]} becomes two [[users]] blocks, and converting it back gives the same array.

Does the converter keep my comments?

No. Both JSON and the TOML parser discard comments during parsing, so there is no way to carry a # comment through a round trip. This is a documented limitation, not a bug. If you need comments preserved, edit the original file by hand rather than round-tripping it through a converter.

Is my data uploaded to a server?

No. The entire conversion — parsing, serialising, and the round-trip check — runs client-side in JavaScript using the smol-toml library and the browser's native JSON engine. Nothing you paste leaves your device, which is why it is safe for config files that contain tokens or internal hostnames.

How accurate is the conversion?

It follows the TOML v1.0.0 specification and JSON RFC 8259 / ECMA-404. Parsing uses smol-toml v1.7.0, which passes the official toml-test compliance suite. After every conversion the tool re-parses its own output and structurally compares it to your input, so any mismatch (beyond the documented date and null edges) is surfaced immediately.

Will it handle a big pyproject.toml or Cargo.toml?

Yes. Real-world config files — pyproject.toml, Cargo.toml, Hugo and Netlify configs, Ruff settings — are tiny by these standards. The input is capped at two million characters as a safety limit, far beyond any normal config, and conversion of a typical file completes in well under a frame.

Developer · Config

TOML to JSON Converter — bidirectional

Convert TOML to JSON and JSON back to TOML right in your browser. Spec-compliant (TOML v1.0.0, JSON RFC 8259 / ECMA-404), with type-mapping notes, error positions, and a round-trip integrity check. No signup, no uploads, sources cited below.

By Induwara Ashinsana— Executive Director, Ryzera TechnologiesUpdated Jun 24, 2026

TOML → JSON converter

Valid · round-trip OK

JSON indent

TOML input15 lines · 262 ch

Runs entirely in your browser — nothing is uploaded.

JSON output25 lines · 397 ch

{
  "project": {
    "name": "my-app",
    "version": "1.0.0",
    "requires-python": ">=3.11",
    "dependencies": [
      "requests",
      "flask"
    ]
  },
  "tool": {
    "ruff": {
      "line-length": 88,
      "target-version": "py311"
    },
    "mypy": {
      "overrides": [
        {
          "module": "tests.*",
          "ignore_missing_imports": true
        }
      ]
    }
  }
}

Round-trip verified

Structure preserved exactly — fully reversible.

Type-mapping notes

No special type conversions in this input — every value maps directly.

Sources cited: TOML v1.0.0 spec · JSON RFC 8259 · smol-toml. Dates become ISO-8601 strings and JSON null keys are dropped when targeting TOML — see the notes above and the FAQ below.

How it works

This is a deterministic format transform, not a calculator. It parses your input into an in-memory data structure, then serialises that structure into the target format. TOML parsing and serialisation use smol-toml (a zero-dependency library that passes the official toml-testsuite); JSON uses the browser's native JSON.parse and JSON.stringify. Everything runs client-side, so your config never leaves the page.

TOML → JSON

Parse the TOML per the v1.0.0 grammar. Tables and inline tables become JSON objects; arrays of tables ([[x]]) become arrays of objects; dotted headers like [tool.ruff] nest accordingly.
Map each scalar: string → string, integer and float → number (JSON does not distinguish the two), boolean → boolean. Because JSON has no date type, every TOML offset date-time, local date-time, local date, and local time is emitted as an ISO-8601 string — the one lossy edge, surfaced in the notes panel.
Serialise with the chosen indentation (2, 4, tab, or minified) and, optionally, alphabetically sorted keys for stable version-control diffs.

JSON → TOML

Parse the JSON per RFC 8259 / ECMA-404. The root must be an object, because TOML's top level is always a table — a bare array or scalar is rejected with a specific message.
Reconcile against TOML's data model. null has no TOML representation, so a null-valued key is omitted (and counted in the notes); a null inside an array is a hard error, because TOML arrays cannot contain one. Arrays whose items are all objects are written as arrays of tables.
Serialise with smol-toml, which emits spec-compliant tables, inline tables, and arrays of tables.

After either direction, the tool runs a round-trip integrity check: it re-parses its own output and structurally compares it to your input, accounting for the two documented lossy edges (dates becoming strings, null keys being dropped). A clean match shows “round-trip verified”; an expected lossy case shows “converted with notes”; anything else is flagged as a mismatch so you know not to trust it. Comments are not preserved in either direction — both parsers discard them.

Worked examples

1 · pyproject.toml snippet → JSON

TOML in

[project]
name = "my-app"
version = "1.0.0"
dependencies = ["requests", "flask"]

[tool.ruff]
line-length = 88

JSON out (indent 2)

{
  "project": {
    "name": "my-app",
    "version": "1.0.0",
    "dependencies": ["requests", "flask"]
  },
  "tool": { "ruff": { "line-length": 88 } }
}

The dotted header [tool.ruff] nests ruff under tool. No dates or nulls, so the round-trip is lossless and fully reversible.

2 · JSON with an array of tables → TOML

JSON in

{
  "server": { "host": "localhost", "port": 8080 },
  "users": [ { "name": "alice" }, { "name": "bob" } ]
}

TOML out

[server]
host = "localhost"
port = 8080

[[users]]
name = "alice"

[[users]]
name = "bob"

An array of objects becomes an array of tables ([[users]]) — the canonical TOML form. Converting it back yields the identical structure.

3 · Typed scalars and the lossy date edge → JSON

TOML in

created = 2026-06-24T10:30:00Z
enabled = true
ratio = 3.14
count = 42

JSON out (indent 2)

{
  "created": "2026-06-24T10:30:00.000Z",
  "enabled": true,
  "ratio": 3.14,
  "count": 42
}

The notes panel reports: 1 offset date-time → ISO-8601 string. Converting this JSON back to TOML produces created = "2026-06-24T10:30:00.000Z" as a string, not a TOML date — expected, because JSON had already lost the date type.

Frequently asked questions

Sources & references

Conversion behaviour was last verified against the TOML v1.0.0 spec, RFC 8259 / ECMA-404, and smol-toml v1.7.0 on 2026-06-24. The three worked examples above round-trip exactly as documented.

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Comments & feedback

Spotted a bug or want an improvement? Tell us — our team reviews every comment, and good ideas get built. Comments are public and anonymous.

Found a bug, an edge case, or a TOML file that doesn't round-trip?

Email me at [email protected] — most fixes ship within 24 hours.