Runs in your browser

Paste a JSON error. Get the cause and the fix.

Works with messages from Chrome, Firefox, Safari, Node and Python, or with the broken JSON itself. Every explanation links to a page with the exact message each runtime prints, from our own test runs.

Paste your error message

Or paste the JSON that failed. It is checked in your browser and not sent anywhere.

Browse all JSON error messages, or scroll down for every tool for JSON, XML, CSV and YAML. Nothing you paste is uploaded.

What SmartJson Does Well

Repair, Then Format

The Fix action repairs the JSON mistakes people actually paste — trailing commas, single quotes, unquoted keys, missing brackets — and closes unbalanced XML tags, then formats the result so you can see what changed.

Your Data Stays Local

Parsing, formatting, and conversion run in your browser tab. There is no upload endpoint behind these tools, which is why they are safe to use on payloads that contain tokens, customer records, or internal hostnames.

Built for Daily Use

Open a file with Ctrl+O, copy output with Ctrl+C, create a shareable link with Ctrl+Shift+S, and download results as a file. Compare tools show two documents side by side with the differences highlighted.

Complete Data Engineering Toolset

Every tool below has its own page explaining what it does, when to use it, and the edge cases it handles.

JSON Tools Hub

Comprehensive JSON manipulation suite including JSON formatter, validator, parser, and editor

JSON Formatter

Fast online JSON formatter & pretty printer

JSON Validator

Validate JSON syntax instantly

JSON Viewer

Interactive JSON tree viewer

JSON Minify

Minify JSON for reduced file size

JSON Stringify

Convert objects to JSON strings

JSON Sorter

Sort JSON keys alphabetically

Data Format Converters

Convert between JSON, CSV, YAML, and XML formats with perfect data integrity

JSON to CSV

Convert JSON arrays to CSV format

CSV to JSON

Transform CSV files to JSON

JSON to YAML

Convert JSON objects to YAML

XML to JSON

Parse XML and convert to JSON

Comparison & Diff Tools

Compare and highlight differences between JSON, XML, CSV, YAML, and Text files

JSON Compare

Deep JSON object comparison

XML Compare

Compare XML documents side-by-side

CSV Compare

Analyze differences in CSV data

YAML Compare

Compare YAML configuration files

Text Compare

Line-by-line text diff tool

XML & Data Format Tools

Format, validate, and process XML, YAML, SOAP, and WSDL documents

XML Formatter

Format and beautify XML with proper indentation

XML Validator

Validate XML syntax and structure

XML Minify

Compress XML by removing whitespace

YAML Formatter

Format YAML configuration files

YAML Validator

Validate YAML syntax online

CSV Formatter

Format and clean CSV data

CSV Validator

Validate CSV file format

SOAP Formatter

Format SOAP XML messages

WSDL Formatter

Format WSDL web service definitions

Guides for Working With Data Formats

Longer write-ups on the problems these tools exist to solve: why a file fails validation, how nested data maps to a spreadsheet, and what actually changes when you minify.

JSON Syntax Guide: Rules and Best Practices

The exact rules a strict parser enforces — quoting, trailing commas, number formats, escapes — and the mistakes behind most "Unexpected token" errors.

JSON to CSV Conversion: Mapping Nested Data to Rows

How to flatten nested objects and arrays into columns without silently dropping fields, and when a single CSV is the wrong target.

CSV Data Integrity: Edge Cases and Special Characters

Embedded commas, quotes, line breaks, encodings, and the spreadsheet auto-conversions that quietly corrupt IDs and dates.

XML vs JSON: Choosing the Right Format

Where each format still wins — attributes, namespaces, and schemas versus size and parsing speed — with realistic examples.

YAML for Configuration: A Practical Guide

Indentation rules, anchors, multi-line strings, and the implicit typing surprises that break CI pipelines and Kubernetes manifests.

Comparing Data Files: Finding the Differences That Matter

Why a text diff misleads on structured data, and how semantic comparison handles reordered keys, whitespace, and moved rows.

All articles →

Frequently Asked Questions

Is my data secure when I use these tools?▼

Yes, absolutely. All processing happens 100% on your device using client-side JavaScript. We never upload or store what you paste. Share links keep their content after the #, which browsers don't send to servers.

Do the tools need a connection once the page has loaded?▼

No. After a tool page has loaded, formatting, validation, conversion, and comparison all run locally, so they keep working if your connection drops. Opening a different tool page does need the network, because pages are not cached for offline use.

What file formats are supported?▼

JSON, XML (including SOAP envelopes and WSDL documents), CSV, and YAML, plus plain text for the Text Compare tool. Converters cover JSON ↔ CSV, JSON ↔ XML, JSON ↔ YAML, CSV ↔ XML, and XML → CSV.

Is there anything to install, or an account to create?▼

No. Every tool runs in a normal browser tab with no extension, download, or sign-up. Useful shortcuts: Ctrl+O opens a file, Ctrl+C with nothing selected copies the input, and Ctrl+Shift+S creates a share link.

Which tools are best for comparing large files?▼

Use the compare tool for your format — JSON, XML, CSV, or YAML Compare — which shows both documents side by side with the changed lines highlighted. Run both files through the matching formatter first so indentation and spacing differences don't drown out the real changes.

Can I convert between different data formats?▼

Yes. Each converter page explains how it handles the awkward cases — nested objects become dotted column names in CSV, repeated XML elements become arrays in JSON, and XML attributes become keys prefixed with @ — so you know what the output will look like before you rely on it.

Start Processing Your Data Today

Pick a tool, paste your data, and get a result in your browser. Free, no sign-up, and nothing you paste leaves your device.