Env Schema Validator

About this tool

A missing or mistyped environment variable rarely fails where you can see it. The app boots, connects to nothing, and dies later with undefined is not a function or a timeout against localhost. This tool moves that failure to the front: you declare what the environment must contain — which keys are required, what type each value has, and which allowed values are legal — and it checks a .env file against that declaration, listing every problem with its line number, a severity and the rule that caught it.

Everything runs locally in your browser via WebAssembly. The .env you paste is never uploaded, and values of secret-looking keys (names containing SECRET, TOKEN, PASSWORD, KEY, AUTH) are masked in the report so a result is safe to paste into an issue or a CI log.

Worked example

Schema:

NODE_ENV=required|enum:development,staging,production
PORT=required|port
DATABASE_URL=required|url
API_KEY=required|min:32
TIMEOUT=number|min:1|max:60|default:30

.env:

# staging
export NODE_ENV=staging
PORT=99999
DATABASE_URL=localhost
API_KEY=short
LEGACY_FLAG=1

Result:

.env schema check: FAILED — 3 errors, 1 warning (5 declared keys, 5 keys in the file)
  line 3    error    type                    'PORT' must be a TCP port between 1 and 65535, got '99999'
  line 4    error    type                    'DATABASE_URL' must be a URL with a scheme and host (e.g. https://api.example.com), got 'localhost'
  line 5    error    min                     'API_KEY' must be at least 32 characters long, got 5
  line 6    warning  unknown-key             'LEGACY_FLAG' is set in the .env file but is not declared in the schema

NODE_ENV=staging passes because staging is in the allowed list, and TIMEOUT is absent without complaint because it is optional and documents a default.

The rules dialect

One KEY=rule|rule:arg line per variable. A bare KEY= line simply means required, so an existing .env.example works as a schema as-is.

Prefer JSON Schema? Paste one instead: type, required, properties with enum, minimum/maximum, minLength/maxLength, pattern, format (uri, email, hostname) and default are all honoured, and the auto format setting detects it by the leading {.

Limits and edge cases

• Only the .env text you paste is examined — the tool never reads process.env, the shell, or any file on disk, and it never rewrites your file.
• Duplicate keys follow dotenv semantics: the last definition wins and is the one validated; the earlier one is reported as a warning.
• ${VAR} interpolation is not expanded — a value like http://${HOST}:${PORT} is checked as the literal text it is, so a url rule on an interpolated value will flag it.
• Comments (#), blank lines, export prefixes, single/double quotes and trailing # comments on unquoted values are all understood.
• min/max on a string counts characters, not bytes.
• There is no practical size cap; a schema with thousands of keys still validates instantly, since everything runs as local WebAssembly.