How do I check if my JSON is valid?

Paste your JSON into the editor and click Validate. The tool checks your JSON against the official RFC 8259 specification and shows exact line numbers and descriptions for any errors found.

What are the most common JSON errors?

The top five JSON errors developers encounter are: trailing commas after the last item, single quotes instead of double quotes, unquoted property names, missing commas between items, and comments (JSON doesn't support comments).

Does JSON allow comments?

No. Standard JSON (RFC 8259) does not support comments of any kind — not //, not /* */, not #. If you need comments, consider JSONC or JSON5 formats, or use our JSON Repair tool to strip comments automatically.

Why does my JSON fail validation even though it looks correct?

Invisible characters are a common culprit. Check for non-breaking spaces, zero-width characters, or BOM markers. Also watch for smart quotes (curly quotes) that text editors sometimes auto-insert.

JSON バリデーター

詳細なエラーと行番号で JSON を検証

Loading editor...

Catch syntax issues before they reach production

A validator tells you exactly where a payload stops being valid JSON. That matters when an AI model emits malformed output, an API returns broken data, a config file breaks a deploy, or a fixture fails in CI and the error message is too vague to trust at a glance.

Use the validator when you need to

Confirm a payload is valid JSON

Run a fast syntax check before you feed the data into an API client, parser, or schema validator.

Pinpoint line and column errors

Find the exact location of missing commas, bad quotes, truncated objects, or other parse failures.

Triage malformed fixtures, config files, and model output

Validate copied request bodies, seed files, local config, and structured AI output before they break a deploy or test run.

How to validate JSON quickly

1
Paste the JSON payload into the editor.
2
Click Validate to run the syntax check and inspect any reported line and column errors.
3
If it fails, repair the payload or apply a suggested fix, then validate again.

Keep going

Repair invalid JSON

Fix common syntax mistakes automatically before validating again.

Understand parser errors

See what common error messages mean and how to resolve them faster.

Learn how to fix invalid JSON

Work through the most common mistakes developers hit in real payloads.

Validate against a schema

Move from syntax validation to contract validation when shape matters too.

Common validator workflows

A model or backend endpoint returns malformed JSON

Paste the response to isolate whether the issue is syntax, truncation, or an unexpected literal.

A copied payload fails in Postman or your app

Validate it first so you know whether the bug is in the JSON or in the request itself.

A fixture breaks your tests

Use the exact error position to repair the file without diffing every line manually.

よくある質問

エディタにJSONを貼り付けて「Validate」をクリックします。ツールは公式仕様RFC 8259に基づいて検証し、エラーがあれば行番号と内容を具体的に表示します。

開発で特に多いのは次の5つです。最後の要素の後ろのカンマ（trailing comma）、ダブルクォートではなくシングルクォート、プロパティ名のクォート漏れ、要素間のカンマ不足、コメントの混入（JSONはコメント非対応）。

いいえ。標準JSON（RFC 8259）はコメントを一切サポートしません（// も /* */ も # も不可）。コメントが必要ならJSONCやJSON5を検討するか、JSON Repairツールでコメントを自動的に削除してください。

不可視文字が原因のことがよくあります。ノーブレークスペース、ゼロ幅文字、BOM（Byte Order Mark）などが混ざっていないか確認してください。また、エディタが自動挿入するスマートクォート（曲がった引用符）にも注意が必要です。