ToolDeck's TOML tools let you format, validate, and convert TOML configuration files directly in your browser — no installation, no account, no data uploaded to any server. The TOML Formatter parses your TOML input and re-serializes it with consistent indentation, normalized key ordering, and inline validation errors that pinpoint syntax problems. The TOML to JSON Converter transforms TOML documents into their JSON equivalents, preserving data types including datetimes, inline tables, and arrays of tables. Both tools run entirely client-side, so your configuration files — which often contain database credentials, API endpoints, and deployment secrets — stay on your machine. If you need the reverse direction, the JSON to TOML Converter in the JSON category handles that conversion.
What Are TOML Tools?
TOML (Tom's Obvious, Minimal Language) is a configuration file format built around explicit, unambiguous syntax. Created by Tom Preston-Werner, co-founder of GitHub, TOML was first released in 2013 and reached its 1.0 specification in January 2021. The format maps unambiguously to a hash table: every TOML file defines a tree of key-value pairs organized into tables (sections marked by [brackets]). Unlike YAML, TOML does not rely on indentation for structure, which eliminates an entire class of whitespace-related parsing bugs. Unlike JSON, TOML supports comments, native date/time types, and multi-line strings — features that configuration files need but JSON was never designed to provide.
TOML tools automate the mechanical work of reading, validating, and converting TOML files. Formatting tools normalize indentation and key ordering so that configuration files stay readable across a team, even when multiple contributors edit the same file. Conversion tools translate between TOML and JSON, which is useful when a library or API expects JSON input but your source of truth is a TOML configuration. Validation catches syntax errors — a missing closing bracket, a duplicate key, or an invalid datetime literal — before they cause failures at application startup.
These tasks come up frequently in Rust projects (where Cargo.toml is the package manifest), Python packaging (pyproject.toml replaced setup.py as the standard build configuration in PEP 518 and PEP 621), Hugo static sites (which use TOML for site configuration by default), and any infrastructure setup that stores config in TOML files. The TOML specification is maintained at toml.io, and parsers exist for every major programming language.
Why Use TOML Tools on ToolDeck?
ToolDeck's TOML tools parse and process everything inside your browser tab using JavaScript. No configuration data is transmitted to a server, no account is required, and the tools work offline after the initial page load.
🔒Private by default
Configuration files often contain sensitive values — database URLs, API keys, deployment targets. ToolDeck processes TOML entirely client-side, so nothing leaves your browser. Safe for proprietary projects and internal infrastructure configs.
⚡Instant feedback
Paste TOML, see formatted output or JSON immediately. Syntax errors are reported with line numbers and descriptions. No waiting for a CLI tool to install or a build step to complete.
🔄Accurate type conversion
The TOML to JSON converter preserves TOML-specific types like offset datetimes, local dates, and local times as ISO 8601 strings. Integer and float precision is maintained. Arrays of tables map correctly to JSON arrays of objects.
🌐No installation required
Works on any device with a modern browser. Useful when you are reviewing a pull request on a machine without your usual development environment, or when you need to quickly validate a colleague's TOML file.
TOML Tools Use Cases
TOML formatting, validation, and conversion come up across different roles and project types. Rust developers work with Cargo.toml daily. Python developers configure builds and tools through pyproject.toml. DevOps engineers manage application configuration that ships as TOML. The tasks below show where browser-based TOML tools save time compared to writing a one-off script or installing a CLI tool.
Cargo.toml cleanup
After merging several dependency additions, a Rust project's Cargo.toml has inconsistent formatting. Run it through the
TOML Formatter to normalize indentation and key order before committing.
pyproject.toml to JSON
A CI pipeline needs build metadata in JSON format, but the source of truth is pyproject.toml. Use the
TOML to JSON Converter to generate the JSON representation and verify the mapping before scripting the conversion into your pipeline.
Config migration
Moving an application from JSON-based configuration to TOML (or vice versa). The
TOML to JSON Converter lets you compare the two representations side by side to confirm that data types, nested structures, and array semantics are preserved.
Syntax debugging
A TOML configuration file fails to parse at application startup with an opaque error message. Paste it into the
TOML Formatter to get specific line and column numbers for the syntax error, plus a description of what the parser expected.
Documentation generation
Writing documentation that includes configuration examples in both TOML and JSON formats. Convert the canonical TOML example through the
TOML to JSON Converter so both versions stay in sync without manual transcription.
Learning TOML syntax
Developers new to TOML can experiment with the format by writing TOML in the
TOML Formatter, seeing validation errors in real time, and comparing the structure against the formatted output. This is faster than reading the spec alone.
TOML Data Types Reference
TOML v1.0 defines the following data types. Each type maps to a specific representation when converted to JSON. The table below covers syntax, examples, and conversion behavior for each TOML type.
| Type | Syntax | Example | JSON mapping |
|---|
| String | "..." or '...' | name = "TOML" | JSON string. Basic strings support escape sequences (\n, \t, \u). Literal strings ('...') treat backslashes as literal characters. |
| Integer | digits, 0x, 0o, 0b | port = 8080 | JSON number. Supports hex (0xDEAD), octal (0o755), binary (0b1010), and underscore separators (1_000). |
| Float | digits with . or e | pi = 3.14159 | JSON number. Supports inf, -inf, and nan (mapped to null or string in JSON, since JSON has no NaN). |
| Boolean | true / false | enabled = true | JSON boolean. Only lowercase true and false are valid. |
| Offset Date-Time | RFC 3339 | 2024-01-15T09:30:00Z | JSON string (ISO 8601). Includes timezone offset. No native JSON datetime type. |
| Local Date-Time | date T time | 2024-01-15T09:30:00 | JSON string. No timezone information. Useful for wall-clock times. |
| Local Date | YYYY-MM-DD | 2024-01-15 | JSON string. Date without time component. |
| Local Time | HH:MM:SS | 09:30:00 | JSON string. Time without date or timezone. |
| Array | [value, ...] | ports = [8080, 8443] | JSON array. TOML arrays can be heterogeneous in TOML v1.0 but must be homogeneous in v0.5. |
| Table | tomlCategoryContent.r10Syntax | [database] | JSON object. Standard tables use [brackets]. Inline tables use curly braces on a single line. |
TOML v1.0.0 specification (toml.io) is the current stable version. Arrays of tables use [[double brackets]] to define repeated table entries, mapping to JSON arrays of objects.
How to Choose the Right TOML Tool
ToolDeck has three tools that work with TOML files. Two are in the TOML category, and one is in the JSON category for the reverse conversion direction. Pick the tool that matches your task.
- 1
If you need to re-indent a TOML file, normalize key ordering, or validate TOML syntax with line-level error reporting → TOML Formatter - 2
If you need to convert a TOML configuration file into JSON for use in APIs, scripts, or tools that expect JSON input → TOML to JSON Converter - 3
If you need to convert a JSON document into TOML format for projects that use TOML as their configuration standard → JSON to TOML Converter
For everyday TOML work, the TOML Formatter handles formatting and validation in a single step — paste your TOML, and it will either produce clean output or tell you exactly where the syntax error is. When you need to bridge TOML and JSON, the TOML to JSON Converter preserves all TOML data types including datetimes and nested tables. For the reverse direction (JSON to TOML), use the JSON to TOML Converter in the JSON category. If you are debugging a configuration that fails to parse, start with the TOML Formatter: its error messages include line numbers and expected-token descriptions that are more specific than what most application-level TOML parsers report.
Frequently Asked Questions
What is the difference between TOML and YAML?
TOML uses explicit bracket syntax for tables and does not rely on indentation for structure. YAML uses indentation to define hierarchy, which makes it sensitive to whitespace errors — a single misplaced space can change the parsed structure entirely. TOML also has native date/time types and prohibits duplicate keys, while YAML silently uses the last value when a key appears twice. TOML is generally preferred for application configuration, while YAML is more common in Kubernetes manifests and CI/CD pipeline definitions where its multi-document support and anchors/aliases are useful.
What is the difference between TOML and JSON?
JSON is a data interchange format designed for machine-to-machine communication. TOML is a configuration format designed for humans to read and edit. TOML supports comments (lines starting with #), native datetime types, multi-line strings, and tables that reduce nesting depth. JSON does not support comments, has no date type, and requires explicit nesting with curly braces. JSON is the right choice for API payloads and data storage; TOML is the right choice for configuration files that humans edit by hand.
Can TOML represent all JSON data structures?
TOML can represent most JSON structures, but there are edge cases. TOML does not support null values — there is no TOML equivalent of JSON null. TOML keys must be strings, which matches JSON object keys. TOML arrays were restricted to homogeneous types in v0.5, but TOML v1.0 allows mixed-type arrays. Deeply nested JSON objects may become verbose in TOML because each nesting level requires a separate table header.
Which projects use TOML for configuration?
Rust's Cargo build system uses Cargo.toml as its package manifest. Python adopted pyproject.toml as the standard build configuration file through PEP 518 (2016) and PEP 621 (2020). Hugo, the static site generator, uses TOML for site configuration by default. InfluxDB uses TOML for its server configuration. The Go module system considered TOML but chose its own format; however, many Go projects still use TOML for application-level config via libraries like BurntSushi/toml and pelletier/go-toml.
How does TOML handle comments?
TOML supports full-line comments and end-of-line comments using the # character. Everything from # to the end of the line is ignored by the parser. Comments cannot appear inside multi-line basic strings or multi-line literal strings. When converting TOML to JSON, comments are discarded because JSON has no comment syntax. This means a round-trip from TOML to JSON and back to TOML will lose all comments from the original file.
What are arrays of tables in TOML?
Arrays of tables use [[double bracket]] syntax to define repeated entries of the same table structure. For example, [[servers]] appearing twice creates an array with two server objects. In JSON, this maps to an array of objects. Arrays of tables are commonly used for lists of dependencies, server definitions, or plugin configurations where each entry has the same set of keys.
Is TOML whitespace-sensitive?
TOML is not indentation-sensitive. Indentation is purely cosmetic and does not affect parsing. However, TOML does require newlines to separate key-value pairs — you cannot put two key-value pairs on the same line (except inside inline tables). Inline tables must fit on a single line and cannot contain newlines. This design avoids the indentation-based bugs that are common in YAML files.
What happens to TOML datetime values when converting to JSON?
JSON has no native datetime type, so TOML datetimes are converted to ISO 8601 strings. Offset datetimes (like 2024-01-15T09:30:00Z) keep their timezone offset in the string representation. Local datetimes, local dates, and local times are each serialized as strings without timezone information. The conversion is lossless in the sense that the original value can be parsed back from the string, but the JSON consumer must know to treat these strings as dates rather than arbitrary text.