⚙️ TOML Formatter & Converter
Format TOML configuration files and convert to JSON
[server] host = "localhost" port = 8080 debug = true [database] url = "postgres://localhost/mydb" max_connections = 25 [features] enabled = ["auth", "api", "admin"]
How to Use the TOML Formatter
TOML (Tom's Obvious Minimal Language) is a configuration file format used by Cargo (Rust), Hugo, Deno, and many other tools. Paste your TOML config into the left panel. Use Format mode to clean up spacing and consistency, or TOML → JSON to convert the config into JSON format (useful when integrating with JSON-based tooling). The converter handles strings, numbers, booleans, and arrays.
Common TOML files: Rust's Cargo.toml (package manifest), Hugo's config.toml, pyproject.toml (Python packaging), Deno's deno.json, and various Rust/Go application configs. TOML's key advantage over YAML is its strict, unambiguous specification - no indentation-sensitive parsing.
What is TOML and which tools use it?
TOML (Tom's Obvious, Minimal Language) is a configuration file format designed to be minimal and readable. Major uses: Rust ecosystem (Cargo.toml for project dependencies and metadata), Python packaging (pyproject.toml replacing setup.py and setup.cfg), Hugo static site generator (config.toml), Gitea and Forgejo (app.ini is TOML-like), uv Python package manager, and various Go applications. TOML is often compared to YAML and INI — it is more readable than JSON for configuration, less whitespace-sensitive than YAML, and more structured than INI files.
What is the difference between TOML, YAML, and JSON for configuration?
TOML: designed for configuration, very human-readable, strict typing (integers, floats, booleans, dates are distinct types), no ambiguity. Each type has explicit syntax. Tables and arrays of tables have unambiguous syntax. YAML: flexible but whitespace-sensitive (indentation errors cause silent failures), many implicit type coercions (yes/no become booleans, 2026-04-15 becomes a date silently). JSON: strict but verbose, no comments allowed, no trailing commas. TOML is the least surprising — its type system is explicit and its syntax is unambiguous. YAML's flexibility makes it error-prone for config files.
What are the TOML data types and how are they written?
Strings: 'single quoted' (literal, no escapes) or "double quoted" (processes escape sequences). Multi-line: triple quotes. Integers: 42, -17, 0xFF (hex), 0o77 (octal), 0b1010 (binary), 1_000_000 (underscores for readability). Floats: 3.14, -0.5, 1e6, inf, nan. Booleans: true, false (lowercase only). Dates: 2026-04-15 (local date), 12:30:00 (local time), 2026-04-15T12:30:00Z (datetime with timezone). Arrays: [1, 2, 3] or multi-line. Tables: [table.name] headers. Arrays of tables: [[array.of.tables]].
How do I represent nested configuration in TOML?
TOML tables use [section] syntax: [database] host = 'localhost' port = 5432. Nested tables: [database.pool] max_connections = 10. Inline tables: database = { host = 'localhost', port = 5432 } — same as the above but on one line. Arrays of tables (for lists of objects like multiple servers): [[servers]] name = 'prod' host = '10.0.0.1' [[servers]] name = 'staging' host = '10.0.0.2'. The [[double bracket]] syntax creates an array entry each time it appears.
How do I convert Cargo.toml TOML to JSON for processing?
This tool converts TOML to JSON. The TOML structure maps to JSON objects (tables → objects, arrays → arrays). After conversion, use the JSON Formatter to validate and the JSONPath Tester to query specific values. For programmatic processing in Rust: serde and toml crates parse Cargo.toml natively. In Python: import tomllib (stdlib in 3.11+) or tomli library. In Node.js: @iarna/toml or smol-toml npm packages. For CI/CD that needs to read Cargo.toml values: toml-query CLI or jq after TOML-to-JSON conversion.
What are common Cargo.toml configuration patterns?
Workspace definition: [workspace] members = ['crate-a', 'crate-b']. Package metadata: [package] name = 'my-crate' version = '0.1.0' edition = '2021'. Feature flags: [features] default = ['std'] async = ['tokio']. Build dependencies: [build-dependencies] cc = '1.0'. Dev dependencies: [dev-dependencies] criterion = '0.5'. Profile optimization: [profile.release] opt-level = 3 lto = true. Patch override: [patch.crates-io] serde = { path = '../serde' }.
What other configuration and format tools are on this site?
The YAML Formatter handles Kubernetes, Docker Compose, and CI/CD config files. The JSON Formatter validates the JSON output from TOML conversion. The Diff Checker compares two TOML file versions before committing changes. The Environment File Parser handles .env files used alongside TOML configs. The Docker Compose Generator creates docker-compose.yml files that often pair with TOML app configs. All are in the Dev Tools section.
📊 Key Data Points
RFC 3339
TOML native datetime format — validated by this tool
v1.0.0
TOML specification version implemented by this parser
[[table]]
Array-of-tables syntax — the TOML feature that most confuses newcomers
TOML Formatter & Validator -- Complete USA Guide 2026
TOML is the configuration format for Rust projects (Cargo.toml), Python packaging (pyproject.toml), and Hugo static sites. It is designed to be unambiguous — but malformed TOML still causes cryptic build failures when types are wrong or table headers are misplaced.
This formatter validates and re-indents TOML and shows the parsed JSON structure. Runs in your browser.
**Long-tail searches answered here:** validate TOML online Cargo.toml free, TOML to JSON converter to check parsed values, TOML syntax checker browser tool no install.
For related config formats, see YAML Formatter.
🔬 How This Calculator Works
Uses a TOML parser running in the browser to parse TOML into a JavaScript object. Catches: invalid date formats, type mismatches, duplicate keys, out-of-order table definitions, and invalid escape sequences.
The JSON view shows the actual data structure your application will see — especially useful for verifying TOML array-of-tables which have a different JSON representation than regular tables.
✅ What You Can Calculate
Cargo.toml and pyproject.toml validation
Validate Rust and Python project configurations before running cargo build or pip install. Catches type errors in version constraints and malformed dependency specifications.
JSON view shows parsed structure
See exactly what your TOML parses to. Array-of-tables vs regular tables have very different JSON representations.
Date and time validation
TOML has native datetime types (RFC 3339 format). This validator checks that your date strings are valid datetimes rather than plain strings.
Duplicate key detection
TOML forbids duplicate keys but some parsers are lenient. This tool catches duplicates that would silently take the last value.
🎯 Real Scenarios & Use Cases
Debugging Cargo.toml errors
cargo build fails with a vague TOML error. Paste your Cargo.toml here to get the exact line and reason.
Writing pyproject.toml configs
Python packaging via pyproject.toml requires exact TOML syntax. Validate here before running pip install.
Hugo site configuration
Hugo config.toml controls site-wide settings. Validate here when adding new parameters.
Comparing with YAML configs
Use this tool and YAML Formatter side by side to compare how the same config looks in TOML vs YAML.
💡 Pro Tips for Accurate Results
Double brackets vs single brackets. [dependencies] defines a single table. [[bin]] defines an array of tables — each section becomes a new element in an array. The JSON view makes this difference immediately clear.
Inline tables are single-line. TOML inline tables must fit on one line — no trailing commas, no multi-line syntax.
String types matter. TOML has four string types: basic, multi-line basic, literal, and multi-line literal. Literal strings treat backslashes as literal characters — useful for Windows paths.
Validate before CI/CD. Paste your Cargo.toml or pyproject.toml here before every commit that touches the config file. A malformed config fails the entire build.
🔗 Use These Together
🏁 Bottom Line
TOML strict typing means errors are caught explicitly rather than silently. This formatter catches type errors, duplicate keys, and ordering problems before they cause cryptic tool failures.
For the full config management workflow: validate here, compare changes with Diff Checker, and check version constraints with Semver Calculator.