JSON tools
Validate manually with Ctrl/Cmd+Enter, or enable automatic checks. Choose a diagnostic location to return to the original line.
Inputs stay in this browser tab; no upload or persistent storage.
Waiting for validation.
JSONC allows // and /* */ comments. Trailing commas remain invalid.
Report outdated or not run. Validate the current input.
Exports contain diagnostics and short source excerpts, not corrected JSON.
An API response can parse successfully and still contain two values for the same field. This JSON validator keeps that evidence visible instead of replacing the first value with the last one. It separates a broken document from a document that deserves a closer look.
Use this JSON syntax checker when debugging a payload or reviewing configuration. You can validate JSON online without reformatting the source. The JSON lint report describes the selected grammar and the locations it actually checked.
A regular JavaScript object cannot retain two members with the same name. Here the scanner reads each member directly from the source. It reports the later occurrence, links it to the first location, and continues through otherwise valid structure. Escaped spellings such as "a" and "\u0061" are compared as the same key.
A long identifier may be legal JSON yet exceed the safe integer range of a consumer using JavaScript Number. The original digits stay in the editor. A warning points to the numeric token; no rounding, quoting or substitution is applied to your document.
Strict JSON is the initial mode. JSONC permits line and block comments, but still rejects trailing commas. Switching modes invalidates the report immediately, so a previous result cannot be mistaken for a check under the new rules.
Line and column numbers start at one. Click a location to move the input cursor there. The reported position is where parsing failed; a missing comma or bracket can originate on an earlier line. Long source excerpts are shortened around the location.
Manual mode supports Ctrl/Cmd+Enter. Automatic mode waits 400ms after the last change and hides the run button. Copy and download are disabled while the report is outdated; export includes every collected diagnostic, not only the first 50 displayed.
The JSON validator distinguishes syntax failure, valid syntax with warnings, and an incomplete check. A duplicate key is an interoperability warning rather than a claim that the JSON grammar forbids it. The same name in different objects is not a duplicate.
Integers outside −9007199254740991 through 9007199254740991 are flagged, including mathematical integers written with a decimal point or exponent. A token that becomes infinity in Number receives a separate overflow warning. This does not certify arbitrary decimal precision.
Diagnostics include a stable code, severity, JSON Pointer, offset, line, column and a short context excerpt. Repeated keys also include the first occurrence. Offsets and columns count UTF-16 units; CRLF counts as one line break. Slash and tilde in pointer segments are escaped.
Syntax validation checks whether text follows the selected grammar. Schema validation checks requirements such as properties and types. This page provides the former plus duplicate-key and numeric-risk diagnostics; a successful result is not evidence of API compatibility.
Inspect the highlighted location and the preceding member or array element. Common causes include a missing comma, a single quote, or text after the root value. Correct the original input and validate again; the tool does not guess a repair.
Select JSONC to permit // and /* */ comments. Trailing commas remain errors, and JSON5 features such as single quotes and unquoted names are unsupported. The report records which mode was used.
The input limit is 500,000 UTF-16 units, not a byte-size promise. Depth, value count, number length and report limits also apply. When a limit interrupts the check, the report explicitly records unknown syntax validity.
Formatting changes indentation; minifying removes insignificant whitespace. Neither is performed here. The JSON validator preserves the text used for every reported position. Use the related formatting tool when you are ready to change its presentation.
Found an unexpected result?
Load the example to compare a repeated-name warning with a numeric-risk warning. The JSON validator lets you inspect each original location before choosing what to change.