JavaScript does not require indentation. A program written on a single line, with no line breaks and no spaces beyond the minimum, will run exactly as well as the same program spread across neatly indented lines, because the language's grammar does not depend on whitespace. But programs are read far more often than they are written, and a reader of unformatted code faces the same problem as a reader of unformatted HTML: the structure is present, but invisible. Where does the loop end? Which statements belong inside the condition? Where does the function return? Formatting answers those questions by making nesting visible.

The JavaScript Formatter and Beautifier tool re-indents and re-spaces JavaScript code you paste in. It breaks the code into lines at block boundaries, indents each nesting level one step further than its parent, and spaces operators and keywords consistently. The result is code a human can follow. The tool works in your browser on pasted text, and it does not run the code, so formatting is always safe to try: nothing executes, and the original text is untouched until you copy the result.

How the tool works

The formatter is token-based. It reads the code as a stream of tokens: identifiers, numbers, strings, operators, and punctuation, rather than as raw characters. It tracks the current nesting depth, increasing it after an opening brace and decreasing it before a closing brace, and it writes each statement on its own line at the current depth. It also applies spacing rules: spaces around operators such as = and +, a space after keywords such as for and if, and no space before semicolons or commas in the usual positions.

Two details of token-based formatting deserve attention, because they are where automatic formatters most often surprise people. The first is the distinction between division and regular expressions. In JavaScript, a forward slash can mean division, as in a / b, or the start of a regular expression, as in /ab+c/g. The formatter guesses which one it is from the previous token: after an operator or keyword, a slash likely starts a regex; after a value, it likely means division. That heuristic works for ordinary code, and the tool preserves a regex such as /ab+c/g intact and renders division as a / b with spaces, but it is a guess, not a full parse, and unusual code can fool it.

The second detail is that the formatter does not validate code. It will re-indent code with a syntax error just as cheerfully as correct code, and the resulting indentation may look odd precisely where the error lies. That oddness is diagnostic, not a defect: a closing brace that lands at an unexpected depth usually marks the spot where a brace was missed or misplaced. Fix the code, then format again, and the indentation should settle into a clean staircase.

A worked example

Start with this compact function, all on one line:

function total(items){let sum=0;for(let i=0;i<items.length;i++){sum+=items[i];}return sum;}

Paste it into the tool and format it. The output is the same function, indented:

function total(items) { let sum = 0; for (let i = 0; i < items.length; i++) { sum += items[i]; } return sum; }

Read it top to bottom. The function opens, and its body is indented one level. The for header sits on one line, with its three parts separated by semicolons and spaces, which is the conventional way to write a loop header. The loop body is indented a second level, and its closing brace lines up with the for keyword. The return statement sits back at the function's level, which correctly shows that it runs after the loop, not inside it. Every structural fact about the function is now visible from the margin alone.

Try the same habit on a real file you have been avoiding. Format a section, then read it without trying to fix anything. You will usually spot one of three things quickly: a statement indented as if it were inside a block when it is actually outside it, a loop body that contains more than you expected, or a return statement that executes earlier than intended. All three are easy to fix once seen, and all three are nearly invisible in unformatted code.

Common mistakes

The first mistake is formatting code and assuming it is now correct. Formatting reveals structure; it does not repair logic. A loop that adds the wrong values still adds the wrong values after formatting, just more readably. The second mistake is formatting generated or minified code and then editing the formatted version as if it were the source. If code is produced by a build step, fix the source and regenerate; the formatted output is for inspection, and your edits to it will be overwritten by the next build.

The third mistake is mixing formatting styles across a project. One file with two-space indentation, another with four, and a third with tabs makes every file look slightly wrong and makes diffs noisy, because a reformatting shows up as a change on every line. Pick one style and let the tool apply it consistently. The fourth mistake is trusting the formatter with regex-heavy code without checking. Because the regex-versus-division guess is heuristic, review any line containing a slash after formatting, and confirm that regex literals survived intact and division expressions still read as division.

A subtler mistake is formatting code that relies on automatic semicolon insertion in unusual ways. JavaScript inserts semicolons in certain positions when they are omitted, and reformatting can change line breaks in ways that alter where insertion happens. If your code omits semicolons deliberately, check the formatted output carefully, or better, write semicolons explicitly so formatting cannot change the program's meaning.

Honest limitations

This tool re-indents and re-spaces pasted JavaScript code in your browser, using token-based rules. It does not validate code, parse it fully, run it, or fix syntax or logic errors. It guesses whether a slash starts a regular expression or means division, based on the previous token, and unusual code can fool that guess. It does not understand every modern syntax construct perfectly, and code using exotic features may be formatted awkwardly rather than correctly. It does not minify, and it does not apply a project's linting rules; for team-wide consistency, a configured formatter in your build remains the better choice, with this tool serving quick, one-off tidying and inspection.

Closing

Format early, format consistently, and read the formatted result as a diagnostic: when the shape looks wrong, the code usually is. For companion tasks, tidy stylesheets with the CSS Formatter and Beautifier tool, shrink finished scripts with the JavaScript Minify tool, and read our guide How to Format and Validate JSON for the same discipline applied to data.