snake_case Converter

What is snake_case?

snake_case is a naming convention where compound identifiers are written in all lower-case with underscores between the words — user_name, max_retry_count, is_logged_in. The name evokes the low, slithering shape of the underscores running along the baseline. It’s the dominant style for variable and function names in Python, Ruby, Rust, Elixir and PHP (for non-class identifiers), and it’s the default for column names in most SQL databases. The convention predates these languages by decades — early Unix shells, C library functions (fopen, strcpy, getpid) and the standard POSIX environment variables all used the same pattern.

When to use snake_case

snake_case has well-understood roles in software and data:

• Variable and function names in Python, Ruby and Rust — user_name, calculate_total(), is_ready. PEP 8 (Python’s style guide), the Ruby community style guide and the official Rust style all specify snake_case for local variables, function names, method names and module names.
• Database column names — created_at, user_id, order_total. PostgreSQL, MySQL and SQLite are case-insensitive for unquoted identifiers but lower-case with underscores is the universal convention. ORMs like Django, Rails and SQLAlchemy map between snake_cased columns and language-native identifiers automatically.
• JSON keys for Python-backed APIs — Django REST Framework, FastAPI and Flask APIs commonly serialise keys in snake_case to match the Python attribute names, in contrast to the camelCase used by JavaScript-backed services.
• Environment variable names (combined with the SCREAMING form) — DATABASE_URL, STRIPE_SECRET_KEY, LOG_LEVEL. Unix shells treat env vars as case-sensitive and the upper-case-with- underscores convention is universal across deployment tooling, Docker, Kubernetes and CI systems.
• File and directory names — user_profile.py, migration_001_add_users.sql, test_authentication.rb. Lower-case with underscores avoids the case-sensitivity bugs that bite teams working across macOS, Linux and Windows.
• URL slugs (sometimes) — though kebab-case (/about-us) is more common for SEO, some sites use snake_case (/about_us). Either is readable; pick one and stick to it across the site.

snake_case vs SCREAMING_SNAKE_CASE: same structural rule (lower-case words separated by underscores) but written in all caps. SCREAMING form is reserved for constants — values that don’t change at runtime — and for environment variables. Python is the canonical example: max_retries is a variable, MAX_RETRIES is a module-level constant, and the convention is universal enough that linters warn when it’s broken.

Examples

A few before/after transforms the tool produces:

• hello world → hello_world
• get user profile → get_user_profile
• max retry count → max_retry_count
• is logged in → is_logged_in
• userFirstName → user_first_name
• my-cool-thing → my_cool_thing
• HTTP Request Handler → http_request_handler

Notice how spaces, hyphens and existing camelCase boundaries are all treated as word separators, and capitals are normalised to lower-case in the result.

How to use this snake_case Converter

1. Type or paste your text into the input box. The snake_case result appears in the read-only output box and updates as you type — no Convert button to click.
2. Tap Load sample if you’d like to see a typical multi-word phrase demonstrating the transform.
3. Tap Copy beside the result to put it on your clipboard, ready to paste into your editor or schema migration.
4. Tap Clear to start over.

For other case styles — UPPERCASE, lowercase, Title Case, camelCase, kebab-case — visit the full Case Converter, or the dedicated landings for each style listed under Related Tools at the bottom of the page.

Privacy

The tool walks the text in a few short steps in JavaScript: split on separators (whitespace, hyphens, existing underscores, camelCase boundaries), lower-case each word, join with underscores. It runs in your browser tab on your device’s CPU, with no network call, analytics, or storage. The text you paste never travels anywhere. You can verify in the browser’s Network tab; the page makes one set of requests when it loads and then nothing.

Compatibility notes

The transform relies on basic string operations and the built-in toLowerCase() method, which has been a JavaScript built-in since the language’s inception. Every browser, every OS, every version handles it the same way — there is nothing to polyfill, no library to load. The Unicode coverage matches the JavaScript engine, which on every modern browser is up to date with the current Unicode release.