Use the free TOML Formatter and Validator below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
Why TOML Files Get Messy
TOML files start clean and get messy over time. One developer writes keys with spaces around the equals sign, another writes them without. Someone pastes a section from another project with different indentation. A table header ends up far from its keys after several edits. None of this breaks the file, because TOML ignores most whitespace, but it makes the file harder to read, and hard-to-read configs are where mistakes hide. A formatter restores a single, consistent layout, and a validator proves the file is actually correct.
Validation matters more than formatting. A missing closing bracket on a table header, a duplicate key, or a value with the wrong type will make a program reject the whole file, often with an error message that points at the wrong line. Checking the file here, before you save it into your project, catches those errors while they are still cheap to fix.
How to Use the Tool
Paste your TOML into the input box. Press Validate only if you just want a verdict: the tool reports valid, with a count of the keys it found, or invalid, with the first error message. Press Format TOML if you want the cleaned-up version in the output box, ready to copy back into your project. The formatted output uses the standard layout produced by the smol-toml library: one key per line, a blank line before each table header, and values written in their canonical form.
Formatting never changes what your config means. It only changes how it looks. Keys stay in the same order within each table, values keep their types, and nested tables keep their structure. If formatting ever changed a value, that would be a bug, so compare the first formatted result against your original and confirm the settings match before you adopt the habit.
Common TOML Errors the Validator Catches
Duplicate keys are the most common error. TOML forbids defining the same key twice in one table, and it also forbids defining a table twice. A pasted block often duplicates a key that already exists above, and the validator flags it immediately. Mismatched brackets are next: a table header like [server without its closing bracket is easy to miss in a long file. Bad values are third: a date written in the wrong shape, a string with an unescaped quote, or a number with two decimal points all fail parsing.
The error message tells you what went wrong, and usually where. Read it literally. If it says a key is already defined, search the file for that key. If it complains about an unexpected character, look at the line it names. Fix one error at a time and re-validate, because the first error can hide later ones, and fixing errors in order is faster than guessing.
Keeping Config Files Tidy as a Team
Agree on one layout and format every config before committing it. When every file looks the same, code review gets faster, because reviewers see real changes instead of whitespace noise. Put formatting into your routine the way you already do for source code: format on save, or format before a commit. The habit costs seconds and prevents the slow drift that turns a tidy config into a puzzle.
Also keep a habit of validating files that you did not write. Configs copied from blog posts, generated by scripts, or merged from another branch are the ones most likely to carry a subtle error. A thirty-second check here beats an hour of debugging a service that refuses to start because of one bad line.
Frequently Asked Questions
Does formatting change my values? No. It only rewrites layout and spacing. Values, keys, and structure stay the same.
What if my TOML is valid but ugly? That is exactly what Format is for. Valid and ugly becomes valid and readable.
Can the validator check a file against a schema? No. It checks syntax only: whether the TOML is well formed. It cannot know whether a particular key is required by your application.
Paste your TOML above, validate it, format it, and commit a config you can read with confidence.