JSON Parse Errors: Read the Message, Jump to the Fix

A directory of JSON parser error messages and the article that explains each one — start with a strict validator, then drill into the specific syntax problem.

When you land here

Your code threw a JSON parser error and you want to find the exact fix. Start by reading the parser's message — the position and the suspicious character are clues. Then jump to the article that explains the underlying mistake, and use the strict validator to confirm the repaired text round-trips through JSON.parse.

Validate JSON syntax (strict, line + column)Fix invalid JSON in your browser

Read the parser message

Every modern JSON parser reports a position and the offending character. Match the message against this list and open the article that covers that exact phrasing.

Unexpected token errors — overviewUnexpected token < — your fetch returned HTMLUnexpected token u — you parsed undefinedUnexpected token o — [object Object] was stringifiedUnexpected end of JSON input — truncated or unclosedUnexpected non-whitespace after JSON — extra data, NDJSON?Unterminated string in JSON — quote opened but never closedBad escaped character in JSON — \x, Windows pathsBad control character in string literal — raw tab/newline[object Object] is not valid JSONExpected double-quoted property name — trailing comma

Fix the underlying mistake

Most parser errors come from one of five recurring syntax problems. The guide for each one explains the cause, the fix, and what to check before re-running the parser.

Fix trailing commas in JSONFix single quotes in JSONFix unquoted keys in JSONFix Unexpected Token errors (guide)Fix Expected Property Name errors

Why strict JSON is strict

JSON looks like a JavaScript object literal, but it is a much smaller grammar. No trailing commas, no comments, no single quotes, no Python-style True/None. The historical references explain why the grammar stayed minimal and how interoperability decisions were made.

RFC 8259 — current JSON standardECMA-404 second editionParsing JSON is a Minefield (parser disagreement)Bishop Fox — JSON interoperability researchTree-sitter JSON grammar — why your editor parses differently from JSON.parse

Recommended path

Tool to guide to blog to reference, in one sequence: open the JSON validator to get the exact line and column, read the guide for the underlying mistake, follow the linked blog article for that error message, then look up the standard that defines the grammar.

  • 1. Tool: /json-validate — confirm the parse error and its position.
  • 2. Guide: /guides/fix-json-unexpected-token — match the symptom to the cause.
  • 3. Blog: /blog/json-parse-unexpected-token — full breakdown of token-level mistakes.
  • 4. Reference: /news/rfc-8259-json-standard — why the grammar is strict.
Open JSON FixCompare JSON changes

JSON repair guides

Topic hubs

  1. Fix Invalid JSON: From 'What's Wrong' to a Clean File
  2. JSON Formatter, Validator, Viewer: Pick the Right Tool
  3. Repair LLM JSON Output: Handling Almost-JSON from AI
  4. Privacy: JSON Tools That Don't Leave Your Browser
  5. JSON Interop: YAML, CSV, XML, JWT, Schema

Specific guides

  1. How to Decode Base64 Strings (and JWT Payloads)
  2. URL Encoding: Percent-Encode Query Parameters and Paths
  3. Convert YAML to JSON (and Avoid Indentation Errors)
  4. Convert JSON to CSV: Flatten an Array of Objects
  5. Convert JSON to XML: Root Elements, Attributes, and Arrays
  6. Escape JSON as a String Literal (and Decode Double-Encoded JSON)
  7. Fix Trailing Comma in JSON
  8. Fix Single Quotes in JSON
  9. Fix Unquoted Keys in JSON
  10. Repair LLM JSON Output
  11. Fix JSON Parse Error: Expected Property Name
  12. JSON vs JS Object Literal: The Key Differences
  13. Validate JSON Before API Requests
  14. JSON Formatter vs JSON Repair
  15. Fix JSON Unexpected Token Errors
  16. JSON to JavaScript Object Converter