Why do I get “Unexpected token } in JSON at position ...”?

This usually happens when braces are mismatched (extra } or missing {), or when a comma is missing between object properties/array items. Use the reported position to check bracket pairing and commas near that area.

How to fix “Unexpected token ' in JSON at position ...”?

JSON requires double quotes (") for strings and keys; single quotes (') are not valid JSON. Replace single quotes with double quotes and escape inner quotes when needed.

What does “Unexpected token u in JSON at position 0” mean?

It often means the input is not JSON (e.g., undefined, an error message, or an HTML page). Make sure you copied the raw response body and that it starts with {, [ or another valid JSON value.

Why do I see “Expected double-quoted property name”?

It means an object key is not wrapped in double quotes (e.g., { a: 1 }). Use standard JSON instead: { "a": 1 }.

Formatting works, but numbers/IDs look wrong. What should I do?

Large integers may exceed JavaScript’s safe integer range (2^53 - 1) and lose precision. Represent IDs as strings, e.g. "id": "9007199254740993".

OnesAPK JSON Formatter In-Depth Guide (with JSONPath)

OnesAPK JSON Formatter is part of the OnesAPK Toolbox. It helps you pretty-print JSON, minify JSON, validate JSON, and extract data with JSONPath.

Think of it as:

[A debugging accelerator] Understand API responses, logs, and configs faster
[A troubleshooting helper] Locate Parsing Error issues with line/column and a pointed snippet
[A privacy-friendly online tool] Runs fully Client-side in your browser

What you will learn (overview)

[How to use it] Format / Minify / Remove Line Breaks / Copy Result / JSONPath queries
[Why it works] JSON syntax rules and the interoperability baseline of RFC 8259
[How to debug] Common Parsing Error messages and practical fixes
[How to level up] Using JSON Schema and structured logging in real projects

Typical use cases (engineering-oriented)

[API debugging] Inspect and normalize responses (missing fields, type changes, deep nesting)
[Log troubleshooting] Quickly locate problematic fields in structured logs
[Config validation] Ensure payloads are strict JSON (avoid failures in strict parsers)
[Data extraction] Use JSONPath to extract key fields from large objects

Quick glossary

[Parsing / Parse Error] Failed JSON parsing and its error output
[Minify / Pretty Print] Compact vs human-readable JSON representations
[Normalization] Converting outputs into a consistent indentation/line-break style
[RFC 8259] The modern JSON standard for interoperability

Related tools

OnesAPK Toolbox (Home) Explore more privacy-friendly, client-side tools
OnesAPK JSON Diff Compare two JSON documents and highlight changes

1) Quick Start: How to Use OnesAPK JSON Formatter

What you can do

Pretty-print JSON: turn minified JSON into readable, indented output, improved by Syntax Highlighting.
Minify JSON: remove unnecessary whitespace for compact payloads.
Validate JSON: parse in real time; if invalid, show a clear error message with line/column and a snippet pointer.
Query with JSONPath: extract array items, fields, or filtered subsets from complex JSON.
Copy Result: copy the formatted output; in the JSON viewer you can also quickly copy a key or its value.

A recommended workflow

Click Format once before deep inspection. Structured indentation makes both reading and JSONPath writing easier.
If you need to paste JSON into pseudo terminals / CLI tools, use Remove Line Breaks to avoid unwanted hard breaks.
Use Minify or Copy Result to export the final JSON into your API client, config files, or logs.

2) JSON Fundamentals: Definition, History, and Why It Matters

JSON (JavaScript Object Notation) is a text-based data interchange format and a widely used form of Data Serialization.

It matters because it is:

[Human-readable] easy to read and write
[Machine-friendly] easy to parse and generate across languages
[Ubiquitous on the Web] the de-facto standard for APIs

In modern Web development you will see JSON everywhere:

[API responses] REST / GraphQL / internal services
[Frontend-backend communication] Fetch/Axios, WebSocket messages
[Configuration] build tools, feature flags, CI parameters
[Logs & analytics] structured logs and event payloads

JSON is standardized by IETF RFCs. Most modern implementations follow RFC 8259. This is important because tolerant parsers differ: a payload that “works locally” may fail in stricter production systems.

3) Common Pain Points (and Why Formatting Helps)

[Pain 1: Minified JSON is unreadable]
- Single-line JSON in responses/logs makes nested structures hard to reason about.
[Pain 2: You get a Parsing Error but can’t locate it]
- Missing commas, wrong quotes, or mismatched braces are common.
- OnesAPK JSON Formatter highlights where the parser fails using line/column and a snippet pointer.
[Pain 3: Escaping and Unicode are confusing]
- \n, \t, \", \\, \uXXXX can hide real mistakes.
[Pain 4: Number precision & type mismatches]
- JSON has only one numeric type (number). Large IDs can exceed JavaScript safe integer range.
[Pain 5: JSON vs JSON5 / JS objects / YAML confusion]
- Comments, single quotes, and trailing commas are not standard JSON and may break strict parsers.

4) Under the Hood: Syntax Rules, RFC 8259, and Format Comparison

JSON syntax essentials

JSON supports a small set of types:

Object: { "key": value }
Array: [ value1, value2 ]
String: must use double quotes "
Number: no NaN / Infinity
Boolean: true / false
Null: null

Common strict rules:

Keys must be strings: { "a": 1 } ✅, { a: 1 } ❌
Strings must use double quotes: "hello" ✅, 'hello' ❌
No comments: // and /* */ ❌
No trailing commas: { "a": 1, } ❌, [1,2,] ❌

What RFC 8259 implies in practice

JSON is Unicode text (commonly UTF-8 on the wire).
Whitespace is allowed for formatting, but it does not change meaning.
The syntax is intentionally strict for interoperability.

JSON vs YAML vs XML (quick comparison)

Dimension	JSON	YAML	XML
Readability	Medium-high	High (but indentation-sensitive)	Medium (verbose tags)
Strictness	High (RFC)	Medium (implementation differences)	High
API ecosystem	De-facto standard	Less common	Niche
Best for	APIs, logs, data exchange	Human-edited configs	Documents, strict schema-heavy systems

5) JSONPath in Practice

Use the JSON Search input to run JSONPath queries against your JSON.

Example JSON:

{
  "store": {
    "book": [
      { "category": "fiction", "price": 8.95 },
      { "category": "tech", "price": 30.0 }
    ],
    "bicycle": { "color": "red", "price": 19.95 }
  }
}

Common JSONPath expressions:

$.store.book – select the book array
$.store.book[0] – select the first item
$.store.book[*].price – select all price fields in the array
$..price – recursively select all price fields
$.store.book[?(@.price > 10)] – filter items by a condition

6) Troubleshooting FAQ: 5 Common Errors and Fixes

Q1: `Unexpected token } in JSON at position ...`

Likely causes
- Extra } or missing {
- Missing comma before the end of an object/array
Fix
- Check bracket pairing around the reported area
- Inspect recent properties/items for a missing ,

Q2: `Unexpected token ' in JSON at position ...`

Likely cause
- Single quotes are not valid in JSON
Fix
- Replace ' with " for strings and keys
- Escape inner quotes with \"

Q3: `Unexpected token u in JSON at position 0`

Likely cause
- The input is not JSON (e.g. undefined, an error message, or an HTML page)
Fix
- Ensure the input starts with { or [ or a valid JSON value
- Copy the raw response body instead of a preview

Q4: `Expected double-quoted property name`

Likely cause
- Unquoted keys like { a: 1 }
Fix
- Use quoted keys: { "a": 1 }

Q5: Formatting “works” but numbers/IDs look wrong

Likely cause
- Large integers may exceed JavaScript’s safe integer range (2^53 - 1)
Fix
- Represent IDs as strings: "id": "9007199254740993"

7) Security & Privacy: Why OnesAPK Is Client-side

When handling API payloads, logs, tokens, cookies, or personal data, privacy matters.

Runs fully in your browser (Client-side)
No server upload: your JSON content is not sent to a backend
Safer for sensitive data: tokens, user data, internal API responses

Best practices:

Avoid pasting sensitive JSON on public/shared machines
Mask fields like token, email, or phone before sharing
Boundary note: this tool does not provide legal/compliance advice; follow your team’s policies when handling production data.

8) Go Further: Turn a Formatter into an Engineering Tool

[Use JSON Schema] Validate required fields and types
[Improve structured logging] Consistent keys reduce debugging time
[Speed up API debugging] Formatting + JSONPath extraction helps you focus on what matters

If OnesAPK JSON Formatter helps your workflow, consider starring it (favorite button on the page) so it’s always one click away.

JSON Formatter