Free Online Validators
Catch syntax and structure errors with the exact line and reason.
1 tool in this section
About Validators
This section currently holds one validator and it is a narrow one: environment files. That is deliberate. A .env file has no schema and no parser to complain at you, so the mistakes in it surface much later, usually as a missing value in production.
The validator reads the file and flags what quietly breaks it: a line with no equals sign, a key that starts with a digit or contains a space, an unclosed quote, a duplicate key silently overriding an earlier one, an unquoted value containing spaces, an empty value, and trailing whitespace that ends up inside the value.
Two other jobs sit alongside the check. Values that look like secrets are masked in the preview so you can share your screen, and a .env.example can be generated from a working file with every value stripped out, ready to commit. A compare view diffs two environment files, which is the fastest way to find what a staging config is missing.
Which One Should You Use?
Checking one file
Paste or upload it into the editor view and read the issues list, which points at the line number behind each problem.
Comparing two environments
Use the compare view with your local file on one side and the deployed one on the other, to see which keys were added, removed or changed.
Preparing a repository
Generate the example file from a working one, so contributors get the full list of keys with none of the values.
Common Questions
Do my secrets get uploaded?
What counts as a duplicate key?
Full Tool Pages
About These Tools
Every tool in this section is free to use on ToolBox, with no account, no signup, and no usage limits. Almost all of them run entirely in your browser, so your files and data never leave your device; the few that have to fetch a page or call a service say so on their own page. Browse the full tool directory for everything else.