The Top 5 Most Common JSON Syntax Errors (And How to Fix Them)

Introduction: The Fragility of the Universal Data Format

In the modern landscape of software engineering, JavaScript Object Notation (JSON) has ascended to a position of absolute ubiquity. It is the metabolic substrate of the internet, the format through which microservices communicate, configurations are declared, and data is persisted in document stores. Its dominance is codified in RFC 8259, a standard that is deceptive in its brevity.[1] Unlike its verbose predecessor XML, JSON’s specification fits on a handful of pages, promising a lightweight, human-readable interchange format. However, this simplicity masks a rigid intolerance for deviation that plagues developers daily.

The years 2024 and 2025 have witnessed a subtle but significant shift in the nature of JSON syntax errors. While the classic pitfalls of manual editing remain—errant commas and unquoted keys—the ecosystem has been complicated by the widespread adoption of Large Language Models (LLMs) for code generation. Tools like ChatGPT, Claude, and GitHub Copilot, while powerful, often hallucinate valid JavaScript syntax into JSON contexts, introducing subtle errors that pass visual inspection but fail catastrophically at runtime.[3] Furthermore, the fragmentation of parser implementations—from the V8 engine in Chrome to Jackson in Java and json in Python—means that a payload accepted by one system may cause a JsonParseException in another, leading to distributed system failures that are notoriously difficult to trace.[5]

The consequences of these errors extend far beyond a simple “syntax error” message in a console. In production environments, a single malformed JSON configuration can halt continuous deployment pipelines, cause mobile applications to crash upon launch, or trigger cascading failures in microservices architectures where error handling for serialization failures is insufficient.[8] For instance, the documented outage involving AppSheet in 2022 was traced back to a single trailing comma in a properties object, a testament to the fragility introduced by strict parsing standards.[8]

This technical report provides an exhaustive analysis of the five most prevalent JSON syntax errors disrupting development workflows today. It moves beyond superficial solutions to explore the underlying mechanics of parsers, the specific divergences in language specifications (JavaScript vs. JSON), and the nuanced error signatures produced by the industry’s most common runtime environments. By dissecting the “symptoms” manifested in Python, Java, and JavaScript, and analyzing the “bad code” through the lens of the RFC standards, this guide equips senior backend engineers and technical architects with the knowledge to diagnose, fix, and prevent these errors with surgical precision.

1. Trailing Commas (The “Ghost” Element)

The trailing comma—often referred to as a “final comma”—stands as the single most frequent syntax violation in the JSON ecosystem. Its prevalence is not due to ignorance, but rather to the muscle memory developed by engineers working in modern programming languages that encourage its use. This error represents a fundamental conflict between the ergonomic conventions of code maintainability and the strict portability requirements of data serialization.

The Mechanism of Failure

To understand why trailing commas are rejected, one must look at the definitions provided in the JSON specification. RFC 8259 defines the structure of an object as a collection of “members.” A member is defined recursively: it is a string (the key), followed by a colon, followed by a value. Crucially, the specification states that members are separated by a value separator—the comma (%x2C).[1] The grammar does not define the comma as a line terminator (like a semicolon in C-family languages) but strictly as a separator between two existing elements. Therefore, a comma implies the existence of a subsequent element. When a parser encounters a comma followed immediately by a closing brace (} or ]), it effectively encounters a “ghost” element that does not exist, causing the tokenizer to fail.

This strictness contrasts sharply with the evolution of ECMAScript (JavaScript). Since ES5, and solidified in ES2017, JavaScript has allowed trailing commas in object literals, array literals, and function parameter lists.[5] The rationale for this in JavaScript is version control hygiene: allowing a trailing comma means that adding a new property to an object requires adding a new line, rather than modifying the previous line to add a comma. This results in cleaner git diff outputs, where only the added lines are highlighted.[5] Python, Go, Rust, and Ruby adopted similar conventions for the same reasons.[9]

However, JSON is not JavaScript. It is a data interchange format designed to be language-independent. The authors of the JSON specification excluded trailing commas to simplify the implementation of parsers in languages that might treat a trailing comma as an indicator of an empty slot or a null value (a “sparse array”). For example, in legacy Internet Explorer versions, [1, 2, ] resulted in an array of length 3 (with the third element being undefined), whereas modern browsers result in length 2. To avoid this ambiguity across thousands of potential client languages, the JSON spec mandates the removal of the trailing comma.[5]

The Symptom

The error messages generated by trailing commas are notoriously diverse, often leading developers to misdiagnose the issue as a problem with the preceding data rather than the punctuation itself.

Chrome Console / Node.js (V8 Engine)

In V8-based environments, the error is often reported as an “Unexpected token.” The parser reads the comma, enters a state expecting a new value (a string, number, boolean, object, or array), and instead encounters the closing bracket.

Uncaught SyntaxError: Unexpected token } in JSON at position...

or in array contexts:

SyntaxError: Unexpected token ] in JSON at position...

Modern versions of Chrome (since version 63) and Node.js have improved strictly, but the error remains fundamentally an “unexpected token” violation.[5] The position indicator typically points to the closing brace, which can be confusing if the developer is looking for a typo in the brace itself rather than the comma preceding it.

Python (json.load / json.loads)

Python’s standard json library is a wrapper around a C-based extension (in CPython) that implements a strict state machine. When it encounters a comma in an object, it transitions to a state expecting property name.

json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 1 column 16 (char 15)

This message is highly specific but requires interpretation. The parser is not explicitly complaining about the comma; it is complaining that the character following the comma was not a double-quote (which would start a new key). It found a closing brace instead. In recent discussions within the Python developer community (specifically CPython issue #113149), there have been efforts to make this error message more descriptive by explicitly stating “No trailing commas allowed in JSON objects,” acknowledging that this is a major pain point for users.[11]

Java (Jackson)

Jackson, the predominant JSON library for the Java ecosystem, throws a JsonParseException.

com.fasterxml.jackson.core.JsonParseException: Unexpected character ('}' (code 125)): was expecting double-quote to start field name at

The logic here mirrors Python’s: the state machine consumed the separator and asserted that a field name must follow. The error message explicitly names the character it found (the closing brace, ASCII code 125) and what it wanted (a double-quote).[12]

The Bad Code

The following JSON object represents a typical configuration file where a developer might have commented out a line or simply added a comma out of habit.

{
  "server_config": {
    "host": "api.production.com",
    "port": 8080,
    "timeout_ms": 5000,
  },
  "features_enabled": [
    "logging",
    "metrics",
    "tracing",
  ]
}

In this example, the comma after 5000 and the comma after “tracing” are fatal syntax errors.

The Fix

To render this payload valid, the commas following the final elements must be excised.

{
  "server_config": {
    "host": "api.production.com",
    "port": 8080,
    "timeout_ms": 5000
  },
  "features_enabled": [
    "logging",
    "metrics",
    "tracing"
  ]
}

The Explanation and Advanced Remediation

The prohibition of trailing commas is absolute in standard JSON. While some parsers offer “lenient” modes—such as Jackson’s JsonParser.Feature.ALLOW_TRAILING_COMMA or Python’s json5 library—relying on these features creates a “works on my machine” hazard.[7] A payload generated with trailing commas might be consumed successfully by a lenient internal service but fail when exposed to a public API client or a web browser that adheres to the strict standard.

For developers dealing with massive configuration files where manual removal is impractical, automated tools are essential.

1. Command Line Tools: The sed utility can be used to scrub trailing commas from files before parsing, though this requires complex regex to avoid stripping commas inside strings. A safer approach is using json5 to parse and json to dump.[15]
2. Editor Configuration: Modern IDEs like VS Code allow setting “JSON: Schemas” that strictly validate .json files while allowing “JSON with Comments” (.jsonc) to be more permissive. However, the file extension often dictates the parsing mode.[16]

The divergence between Python code (where {‘a’: 1,} is valid) and JSON data (where {“a”: 1,} is invalid) confuses automated scripts. A common pattern in Python scripts generating JSON is to iteratively append strings ending in commas to a buffer. This requires logic to remove the final comma before closing the bracket, a classic “fencepost error” source.[17]

2. Unquoted Keys (The JavaScript Object Literal Confusion)

The second most pervasive error involves the use of unquoted keys (property names). This error is a direct artifact of the mental model overlap between JSON and JavaScript. In JavaScript, the object { name: “value” } is perfectly valid because name is treated as an identifier. In JSON, however, keys are data, not identifiers, and must be explicitly defined as strings.[6]

The Mechanism of Failure

This error frequently manifests when developers copy output directly from a browser’s debugging console. Chrome and Firefox consoles often pretty-print objects by stripping quotes from keys to improve readability (e.g., displaying {id: 123} instead of {“id”: 123}). When a developer copies this output and attempts to paste it into a .json file or send it as a payload, the parser rejects it immediately.[19]

The JSON specification (RFC 8259, Section 4) is unambiguous: “A name is a string.” Section 7 defines a string as beginning and ending with quotation marks.[1] This design decision simplifies the parser significantly. If quotes were optional, the parser would have to implement full identifier resolution rules (handling spaces, reserved keywords like true, null, function) to distinguish keys from values. By mandating quotes, JSON ensures that any string, including those containing spaces or special characters, can serve as a key without ambiguity.[1]

The Symptom

Chrome Console / Node.js

The JavaScript parser expects a string (starting with ”) as the key. When it sees a letter or number instead, it throws an unexpected token error.

Uncaught SyntaxError: Unexpected token u in JSON at position[2]

In this example, the parser encountered the u of an unquoted key like user instead of a quote.

Python

Python’s error message is perhaps the most helpful here, as it explicitly states the requirement.

json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

The error typically occurs immediately after the opening brace {, as the first token the parser looks for is the key.[20]

Java (Jackson)

Jackson provides a low-level character analysis of the failure.

com.fasterxml.jackson.core.JsonParseException: Unexpected character ('n' (code 110)): was expecting double-quote to start field name at

Here, Jackson explicitly notes that it encountered character code 110 (ASCII for ‘n’) and was expecting a double-quote. This error is common in log processing pipelines (e.g., Graylog) where application logs might dump objects using toString() methods that produce unquoted keys, causing ingestion failures in the JSON parser.[21]

MySQL (JSON_EXTRACT)

In database contexts, using unquoted keys in path expressions or JSON columns can lead to cryptic failures.

Invalid JSON text: "The document is empty." at position 0 in value for column 'tablename.fieldnames'.

Or, if using JSON_EXTRACT, failing to quote keys with spaces or special characters in the path selector (e.g., $.my-field instead of$.“my-field”) will result in SQL syntax errors.[23]

The Bad Code

The following example looks like standard JavaScript or HJSON (Human JSON) but fails as JSON.

{
  userId: 8821,
  access_token: "x8s7s9d8s7d",
  preferences: {
    theme: "dark",
    notifications: true
  }
}

The Fix

Every property name must be wrapped in double quotes.

{
  "userId": 8821,
  "access_token": "x8s7s9d8s7d",
  "preferences": {
    "theme": "dark",
    "notifications": true
  }
}

The Explanation and Advanced Remediation

The insistence on quoted keys allows JSON to be “context-free.” A parser does not need to know the list of reserved words in the host language to parse the data. For example, {“class”: “Math”} is valid JSON, but class is a reserved keyword in Java and JavaScript. If quotes were not required, class: “Math” could confuse a parser into thinking a class definition was starting.

For developers dealing with large datasets of “dirty” JSON (unquoted keys), standard parsers will not suffice.

1. JSON5: The JSON5 standard is a superset of JSON that allows unquoted keys (and trailing commas). Libraries exist for Python (pip install json5), Node.js, and Java to parse this format.[14]
2. Demjson: In the Python ecosystem, demjson is a robust library capable of parsing “fuzzy” or non-strict JSON, including JavaScript object literals.[18]
3. Jackson Configuration: For Java developers, the JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES can be enabled in the ObjectMapper. While this solves the immediate crash, it produces non-standard output if the writer is also configured loosely.[26]

3. Single Quotes vs. Double Quotes (The Python/LLM Discrepancy)

The distinction between single (’) and double (”) quotes is often treated as a stylistic choice in scripting languages. In JSON, it is a hard syntax constraint. This error has surged in prevalence during 2024 and 2025 due to the increasing reliance on Python for backend data processing and the idiosyncrasies of Large Language Model code generation.

The Mechanism of Failure

There are two primary vectors for this error:

1. Python’s String Representation: In Python, the string representation of a dictionary (produced by str() or print()) defaults to single quotes: {‘key’: ‘value’}. Developers frequently make the mistake of stringifying a dictionary using str(data) and writing it to a file or API response, thinking they have created JSON. They have not; they have created a Python string representation.[28]
2. LLM Hallucinations: Research into LLM behavior indicates that models often struggle to distinguish between the quoting requirements of the host language (e.g., Python) and the embedded format (JSON). An LLM asked to “generate a Python script that sends a JSON payload” might hallucinate a payload using single quotes because it is valid Python syntax, unaware that the receiving API will reject it.[3] Benchmarks show a marked decrease in code quality and syntax adherence when models are forced to output structured JSON compared to plain Markdown.[3]

The Symptom

Chrome Console (JSON.parse)

Standard web parsers treat the single quote as an unrecognized token at the start of a string.

Uncaught SyntaxError: Unexpected token ' in JSON at position[1]

The parser expects the double quote ” (ASCII 34) to start a string or key. Seeing ’ (ASCII 39) causes an immediate halt.[5]

Python (json.load)

When Python attempts to load a file formatted with single quotes, it fails with the same error as unquoted keys, because it does not recognize the single quote as a delimiter.

json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

This often leads to confusion for Python developers who see a valid-looking dictionary structure and cannot understand why json.load rejects it.[32]

Java (Jackson)

Jackson is explicit about the character mismatch.

com.fasterxml.jackson.core.JsonParseException: Unexpected character (''' (code 39)): was expecting double-quote to start field name

It specifically identifies code 39 (the single quote) as the offender.[34]

The Bad Code

This snippet is a valid Python dictionary or JavaScript object, but invalid JSON.

{
  'status': 'active',
  'response': {
    'code': 200,
    'message': 'Success'
  }
}

The Fix

All single quotes used as delimiters must be converted to double quotes.

{
  "status": "active",
  "response": {
    "code": 200,
    "message": "Success"
  }
}

Python Remediation:

The correct way to generate JSON in Python is never to use str(), but always json.dumps().

import json

data = {'status': 'active'}

# INCORRECT: Produces single quotes -> "{'status': 'active'}"
invalid_json = str(data)

# CORRECT: Produces double quotes -> "{\"status\": \"active\"}"
valid_json = json.dumps(data)

The Explanation and Advanced Remediation

RFC 8259 Section 7 mandates that all strings be enclosed in quotation marks (”). The rationale is consistency and compatibility with C-based languages where single quotes usually denote a single character (char), not a string.[1]

Recovering Malformed Data:

If a developer is stuck with a massive log file containing single-quoted JSON (often from Python logs), simply doing a find-and-replace (’ -> ”) is dangerous. It will corrupt text containing apostrophes (e.g., “User’s data” becomes “User”s data”).

1. ast.literal_eval (Python): This function allows safely evaluating a string containing a Python literal (like a dictionary) into an object. It is safer than eval() but slower than json.loads(). Once loaded, it can be dumped back out as valid JSON.[29]
2. Jackson Configuration: Java developers can configure the ObjectMapper with JsonParser.Feature.ALLOW_SINGLE_QUOTES to accept this format during ingestion.[35]
3. LLM Post-Processing: For AI-generated content, using a “repair” step with a library like json_remedy (Elixir) or similar Python tools is increasingly becoming a standard part of the “LLM Ops” pipeline to sanitize model outputs before they hit the application logic.[36]

4. Undefined, NaN, and Infinity (The Numeric Gap)

JSON’s number specification is significantly more restrictive than the IEEE 754 floating-point standard used by most modern programming languages. This creates a dangerous “impedance mismatch” where valid numeric calculations in a backend application result in serialization errors when converted to JSON.[38]

The Mechanism of Failure

In languages like Python, Java, and JavaScript, operations like dividing by zero (in floats) or missing data handling can result in special values: NaN (Not a Number), Infinity, or -Infinity.

• Python: float(‘nan’), float(‘inf’)
• JavaScript: Number.NaN, Infinity

A critical implementation detail in Python’s json library exacerbates this issue. By default, Python’s json.dumps() allows these values and serializes them as unquoted literals: NaN, Infinity, -Infinity. This behavior violates the JSON specification, which only allows finite numbers.[1] Consequently, a Python backend can produce “JSON” responses that are technically invalid, causing frontend JavaScript clients or downstream Java consumers to crash.[39]

The Symptom

Chrome Console (JSON.parse)

Since NaN and Infinity are not enclosed in quotes, the parser attempts to interpret them as literals. However, the only unquoted literals allowed in JSON are true, false, and null.

Uncaught SyntaxError: Unexpected token N in JSON at position...

The parser sees the N of NaN (or I of Infinity) and rejects it as an invalid start to a value.[40]

Java (Jackson)

Jackson is strict by default and flags these tokens as non-standard extensions.

com.fasterxml.jackson.core.JsonParseException: Non-standard token 'NaN': enable JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS to allow

This error is common in data engineering pipelines (e.g., Spark or Hadoop jobs) processing scientific data where NaN is used to represent missing metrics.[41]

Graphite / Metrics APIs

This issue is historically prevalent in monitoring systems like Graphite, which had to decide whether to render “inf” as a massive number (to overflow the parser correctly) or as a string, often leading to breakage in JS consumers consuming the API.[43]

The Bad Code

A JSON payload generated from a scientific application or metric aggregator:

{
  "sensor_id": "temp_01",
  "current_value": 23.5,
  "average_load": NaN,
  "peak_load": Infinity
}

The Fix

The fix depends on the semantic meaning of NaN in the specific application context.

Strategy A: Use null (Standard Compliance)

If NaN implies “missing data” or “undefined,” mapping it to null is the most compliant approach.

{
  "sensor_id": "temp_01",
  "current_value": 23.5,
  "average_load": null,
  "peak_load": null
}

Strategy B: Use Strings (Preserve Semantics)

If the distinction between Infinity and null is critical (e.g., in mathematical applications), wrap the values in quotes.

{
  "sensor_id": "temp_01",
  "current_value": 23.5,
  "average_load": "NaN",
  "peak_load": "Infinity"
}

The Explanation and Advanced Remediation

The JSON specification excludes NaN and Infinity largely for portability and security. Parsing these values often implies specific floating-point behavior that not all potential JSON consumers (e.g., COBOL parsers, simple config readers) might support. Furthermore, allowing identifiers like NaN could open the door to ambiguity if a user defined a variable named NaN in a script executing via eval() (though eval() is universally condemned today).[38]

Python Prevention:

To prevent Python from generating invalid JSON, developers should explicitly set the allow_nan parameter.

import json
data = {"value": float('nan')}
# This will raise a ValueError instead of outputting invalid JSON
json.dumps(data, allow_nan=False)

This forces the developer to handle the bad data upstream, perhaps by converting it to None (which becomes null) before serialization.

Java Configuration:

For valid ingestion of non-standard JSON, Jackson provides the JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS flag. This allows the parser to accept NaN and map it to Double.NaN in Java, bridging the gap between the two environments.[41]

5. Hidden Characters (The Copy-Paste “Gremlins”)

The final syntax error is the most insidious because it is often invisible to the human eye. It involves the presence of non-printing characters—specifically the Zero Width Space (U+200B)—embedded within the JSON source.

The Mechanism of Failure

This error is a distinct artifact of “Copy-Paste Development.” It occurs when developers copy code snippets from:

1. Browser Inspector Tools: When inspecting HTML elements in Chrome or Firefox, the browser often inserts zero-width spaces (\u200b) into long strings or attributes to facilitate soft text wrapping for display purposes. If a developer double-clicks and copies this data, the invisible characters are carried over into the clipboard.[44]
2. Rich Text Environments: Copying JSON from Jira tickets, Slack messages, or Confluence pages often brings along hidden formatting characters.
3. Platform-Specific Issues: Certain platforms, like OutSystems, have been known to inject zero-width spaces into usernames or generated HTML, which then propagate into JSON payloads.[45]

The JSON specification defines whitespace very strictly as four specific characters: space (0x20), horizontal tab (0x09), line feed (0x0A), and carriage return (0x0D).[1] Any other character outside of a string literal is treated as a token. When the parser encounters a zero-width space between a key and a colon, for example, it interprets it as an illegal token, not whitespace.

The Symptom

Chrome Console (JSON.parse)

The error message is often baffling because the position indicator points to a valid character or an empty space.

Uncaught SyntaxError: Unexpected token in JSON at position X

In some advanced terminals or editors, the character might render as a red dot or a generic “unknown character” box, but often it is completely invisible, leading developers to stare at “perfect” code that refuses to parse.[44]

Python (json.load)

Python’s decoder detects the character as an invalid control character.

json.decoder.JSONDecodeError: Invalid control character at: line 1 column X (char X)

If the character is inside a string, Python might report a UnicodeEncodingError if the terminal or file encoding is set to something other than UTF-8 (like charmap on Windows).[47]

Java (Jackson)

Jackson will identify the specific unicode code point.

com.fasterxml.jackson.core.JsonParseException: Unexpected character (code 8203 / 0x200b)

Code 8203 is the decimal representation of 200B.[48]

The Bad Code

The following JSON contains a zero-width space immediately after the key “host”. It is impossible to see here, just as it is in your IDE.

{
  "host": "127.0.0.1",​
  "port": 8080
}

The Fix

Since the character is invisible, manual deletion is unreliable—you might delete the visible space but leave the zero-width space. The reliable fix involves sanitization via Regular Expressions or using an IDE feature to “Render Whitespace.”

JavaScript Remediation:[49]

// Remove Zero Width Space (U+200B) and Zero Width No-Break Space (U+FEFF)
const cleanJson = rawInput.replace(/[\u200B\uFEFF]/g, '');
const data = JSON.parse(cleanJson);

Python Remediation:[48]

import re
# Regex to strip specific unicode hidden characters
clean_json = re.sub(r'[\u200b\ufeff]', '', raw_input)
data = json.loads(clean_json)

The Explanation

The existence of the Zero Width Space is a feature of Unicode designed for typesetting (defining where a line could break in languages that don’t use spaces). However, in the context of a data interchange format like JSON, it acts as data corruption. The parser operates on a byte stream; 0x20 (Space) instructs it to skip to the next token, but 0xE2 0x80 0x8B (the UTF-8 encoding of U+200B) is seen as unexpected input bytes.[1]

Modern text editors (VS Code, Sublime Text, JetBrains) have introduced settings to “Highlight Invisible Characters” specifically to combat this issue. Enabling these settings is a recommended practice for any developer working with copied data.[16]

---

Comparison of Parser Behaviors

To aid in debugging, the following table summarizes how the three major parsing environments respond to these top 5 errors. Note how the terminology differs, potentially obscuring the root cause.

Error Type	Chrome / Node.js (V8)	Python (json)	Java (Jackson)
Trailing Comma	Unexpected token }	Expecting property name enclosed in double quotes	Unexpected character ('}')
Unquoted Keys	Unexpected token [char]	Expecting property name enclosed in double quotes	Unexpected character ([char]): was expecting double-quote
Single Quotes	Unexpected token '	Expecting property name enclosed in double quotes	Unexpected character (''')
NaN / Infinity	Unexpected token N / I	Accepted (by default writer); Reader typically accepts unless strict.	Non-standard token 'NaN'
Hidden (U+200B)	Unexpected token (at pos)	Invalid control character	Unexpected character (code 8203)

Conclusion: The Cost of Compliance

The prevalence of these JSON syntax errors highlights a fundamental tension in modern software development: the gap between the flexible, human-centric environments we write code in and the rigid, machine-centric protocols we use to transmit it. While the JSON specification has remained stable, the tools generating it have evolved, introducing new vectors for error—from the helpful-but-illegal trailing commas of Python to the hallucinated syntax of LLMs.

Resolving these issues requires more than just applying a quick fix; it demands a shift in workflow. Developers must treat JSON not as a subset of JavaScript, but as a distinct, strict format. This means adopting rigorous tooling—schema validators, configured linters, and reliable sanitization libraries—and rejecting the temptation to rely on “lenient” parser modes that compromise interoperability. As systems become increasingly interconnected, the “strictness” of your JSON parsing logic becomes a direct proxy for the reliability of your architecture. By understanding the mechanical failures behind these common errors, engineering teams can inoculate their systems against the fragility of the world’s most popular data format.

Sources

1. RFC 8259 - The JavaScript Object Notation (JSON) Data Interchange Format, accessed: november 18, 2025, https://datatracker.ietf.org/doc/html/rfc8259
2. JSON - Wikipedia, accessed: november 18, 2025, https://en.wikipedia.org/wiki/JSON
3. LLMs are bad at returning code in JSON - Aider, accessed: november 18, 2025, https://aider.chat/2024/08/14/code-in-json.html
4. Crafting Structured {JSON} Responses: Ensuring Consistent Output from any LLM, accessed: november 18, 2025, https://dev.to/rishabdugar/crafting-structured-json-responses-ensuring-consistent-output-from-any-llm-l9h
5. Trailing commas - JavaScript - MDN Web Docs, accessed: november 18, 2025, https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Trailing_commas
6. Handling non-compliant JSON with Jackson | by @cowtowncoder | Medium, accessed: november 18, 2025, https://cowtowncoder.medium.com/handling-non-compliant-json-with-jackson-ad0047097392
7. Can not deserialize json to enum value with Object-/Array-valued input, @JsonCreator · Issue #3280 · FasterXML/jackson-databind - GitHub, accessed: november 18, 2025, https://github.com/FasterXML/jackson-databind/issues/3280
8. JSON parse error - AppSheet Q&A - Google Developer forums, accessed: november 18, 2025, https://discuss.google.dev/t/json-parse-error/84474
9. Can json.loads ignore trailing commas? - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/23705304/can-json-loads-ignore-trailing-commas
10. JSON w/ trailing commas would be nice. : r/ProgrammerHumor - Reddit, accessed: november 18, 2025, https://www.reddit.com/r/ProgrammerHumor/comments/tg9oo7/json_w_trailing_commas_would_be_nice/
11. Improving error message with trailing comma in json · Issue #113149 · python/cpython, accessed: november 18, 2025, https://github.com/python/cpython/issues/113149
12. JSON.NET throwing exception on missing comma - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/21469904/json-net-throwing-exception-on-missing-comma
13. Why is JSON invalid when commas in string? - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/24295965/why-is-json-invalid-when-commas-in-string
14. Converting Minecraft NBT Data into Valid JSON for JavaScript Applications - Medium, accessed: november 18, 2025, https://medium.com/@python-javascript-php-html-css/converting-minecraft-nbt-data-into-valid-json-for-javascript-applications-0d2fb36a1891
15. Remove trailing commas from invalid json (to make it valid) - Unix & Linux Stack Exchange, accessed: november 18, 2025, https://unix.stackexchange.com/questions/485004/remove-trailing-commas-from-invalid-json-to-make-it-valid
16. intellij idea - How to display hidden characters by default (ZERO WIDTH SPACE ie. ​), accessed: november 18, 2025, https://stackoverflow.com/questions/9868796/how-to-display-hidden-characters-by-default-zero-width-space-ie-8203
17. Can you use a trailing comma in a JSON object? - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/201782/can-you-use-a-trailing-comma-in-a-json-object
18. python - Bad JSON - Keys are not quoted - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/34812821/bad-json-keys-are-not-quoted
19. JSON: How to create an undefined or NaN value? - dbj( org ), accessed: november 18, 2025, https://dbj.org/json-how-to-create-an-undefined-value-or-an-nan-value/
20. Python can’t parse JSON with extra trailing comma - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/52636846/python-cant-parse-json-with-extra-trailing-comma
21. Json Parser Exception with unquoted Field Names in Graylog 3.01 · Issue #5852 - GitHub, accessed: november 18, 2025, https://github.com/Graylog2/graylog2-server/issues/5852
22. Jackson : was expecting double-quote to start field name - Mkyong.com, accessed: november 18, 2025, https://mkyong.com/java/jackson-was-expecting-double-quote-to-start-field-name/
23. MySQL JSON_EXTRACT path expression error - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/35735454/mysql-json-extract-path-expression-error
24. MySQL 9.2 Reference Manual :: 13.5 The JSON Data Type, accessed: november 18, 2025, https://dev.mysql.com/doc/refman/9.2/en/json.html
25. Safely parsing a JSON string with unquoted keys - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/4210160/safely-parsing-a-json-string-with-unquoted-keys
26. java - ALLOW_UNQUOTED_FIELD_NAMES in jackon JSON library - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/4815231/allow-unquoted-field-names-in-jackon-json-library
27. How to let jackson generate json string using single quote or no quotes? - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/14010754/how-to-let-jackson-generate-json-string-using-single-quote-or-no-quotes
28. Python requests library: a response returns single quoted JSON - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/33418874/python-requests-library-a-response-returns-single-quoted-json
29. Decoding Json String with Single Quotes in Python - GeeksforGeeks, accessed: november 18, 2025, https://www.geeksforgeeks.org/python/decoding-json-string-with-single-quotes-in-python/
30. Leveraging LLMs for Automated Correction of Malformed JSON | by Lilian Li - Medium, accessed: november 18, 2025, https://medium.com/@lilianli1922/leveraging-llms-for-automated-correction-of-malformed-json-e3c1f8b789a6
31. How to make JSON parse a JSON string containing single quotation marks - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/56479058/how-to-make-json-parse-a-json-string-containing-single-quotation-marks
32. Why can I not deserialise a JSON string with single quotes in Python? - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/69432658/why-can-i-not-deserialise-a-json-string-with-single-quotes-in-python
33. Help: json.loads() cannot parse valid json - Page 2 - Python Discussions, accessed: november 18, 2025, https://discuss.python.org/t/help-json-loads-cannot-parse-valid-json/12605?page=2
34. Configure Jackson to deserialize single quoted (invalid) JSON - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/6591388/configure-jackson-to-deserialize-single-quoted-invalid-json
35. Jackson Exceptions - Problems and Solutions | Baeldung, accessed: november 18, 2025, https://www.baeldung.com/jackson-exception
36. nshkrdotcom/json_remedy: A practical, multi-layered JSON repair library for Elixir that intelligently fixes malformed JSON strings commonly produced by LLMs, legacy systems, and data pipelines. - GitHub, accessed: november 18, 2025, https://github.com/nshkrdotcom/json_remedy
37. JsonRemedy - A blazingly fast, Elixir-native JSON repair library, accessed: november 18, 2025, https://elixirforum.com/t/jsonremedy-a-blazingly-fast-elixir-native-json-repair-library/71174
38. JSON left out Infinity and NaN; JSON status in ECMAScript? - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/1423081/json-left-out-infinity-and-nan-json-status-in-ecmascript
39. sending NaN in json - python - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/6601812/sending-nan-in-json
40. NaN - JavaScript - MDN Web Docs, accessed: november 18, 2025, https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN
41. Non-standard token ‘NaN’ - Dremio community, accessed: november 18, 2025, https://community.dremio.com/t/non-standard-token-nan/637
42. Parse NaN Json.parse configuration - scala - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/55623908/parse-nan-json-parse-configuration
43. json with Infinity values is invalid · Issue #813 - GitHub, accessed: november 18, 2025, https://github.com/graphite-project/graphite-web/issues/813
44. u200b (Zero width space) characters in my JS code. Where did they come from?, accessed: november 18, 2025, https://stackoverflow.com/questions/7055600/u200b-zero-width-space-characters-in-my-js-code-where-did-they-come-from
45. ZeroWidthSpace found in user name when inspecting HTML - OutSystems Support, accessed: november 18, 2025, https://success.outsystems.com/support/troubleshooting/incident_models/incident_models_outsystems_developer_cloud/zerowidthspace_found_in_user_name_when_inspecting_html/
46. What is this red bullet/dot in my JSON response in chrome developer tools? - Reddit, accessed: november 18, 2025, https://www.reddit.com/r/webdev/comments/1yfnto/what_is_this_red_bulletdot_in_my_json_response_in/
47. Adding zero width characters to strings - python - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/49600250/adding-zero-width-characters-to-strings
48. ZERO WIDTH SPACE in Json - java - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/37194215/zero-width-space-in-json
49. Remove zero-width space characters from a JavaScript string - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/11305797/remove-zero-width-space-characters-from-a-javascript-string
50. Zero Width Space character in string literals: Detect and/or prevent - Stack Overflow, accessed: november 18, 2025, https://stackoverflow.com/questions/32013346/zero-width-space-character-in-string-literals-detect-and-or-prevent