The error message json decoder jsondecodeerror expecting property name enclosed in double quotes appears when a JSON parser encounters a structure that does not conform to the JSON specification. Here's the thing — in practical terms, the parser is telling you that it expected to see a property name—a string that identifies a field—surrounded by double quotation marks, but instead it found something else, such as an unquoted identifier, a single quote, or an unexpected character. This mismatch can arise from a variety of sources, ranging from simple typographical mistakes to more subtle issues involving encoding or formatting It's one of those things that adds up..
When a JSON parser throws the “expecting property name enclosed in double quotes” error, it is signaling that the token it just read cannot serve as a key in an object. Below are the most common scenarios that trigger this condition, followed by a systematic approach to locate and fix the problem, and finally a set of preventive measures you can adopt in your codebase.
Typical Sources of the Error
| Category | What Happens | Why It Breaks JSON |
|---|---|---|
| Missing quotes around a key | { name: "Alice", age: 30 } |
JSON requires every object key to be a string literal ("name"). Still, |
| Misplaced brackets/braces | { "items": [ "a", "b" ] , } (extra comma before ]) or { "items": [ "a", "b" ] } ] |
Mis‑nesting causes the parser to be in the wrong context when it reads the next token, often interpreting a value as a key. So |
| Trailing commas | { "name": "Alice", } |
A comma after the last element signals that another value (or key) should follow; the parser then encounters the closing brace and expects a key. Here's the thing — |
| Incorrect encoding | A UTF‑8 file saved as UTF‑16LE without a BOM, causing the first byte to be read as 0xFF |
The parser sees a stray byte before the opening { and treats it as part of a key, leading to the same error message. Even so, |
| Single‑quoted strings | { 'name': "Alice" } |
Only double quotes (") are permitted for strings in JSON. Bare identifiers are legal in JavaScript object literals but not in JSON. |
| Control characters or invisible bytes | { "name": "A\u000lice" } (where \u0000 is a null byte) |
Non‑printable control characters inside a string break the tokenisation step; the parser may interpret the following character as the start of a new key. Single quotes are treated as invalid characters. |
| Concatenated or fragmented JSON | {"id":1}{"id":2} (two objects back‑to‑back) |
After finishing the first object, the parser expects either the end of input or a comma separating array elements; seeing another { makes it think a new key should start. |
| Comment tokens | { // note\n "name": "Alice" } |
JSON does not support comments; the slash is read as an unexpected character while looking for a key. |
Step‑by‑Step Debugging Procedure
-
Capture the Exact Payload
- Log the raw string that is being fed to
json.loads/JSON.parse(or whatever parser you use). - If the data comes from a network request, enable verbose logging or use a tool like Wireshark/Charles to see the exact bytes.
- Log the raw string that is being fed to
-
Validate the First Few Characters
- Ensure the string starts with
{(for an object) or[(for an array) and ends with the matching closing bracket. - Strip any leading/trailing whitespace or BOM (
\uFEFF) before parsing.
- Ensure the string starts with
-
Use a JSON Linter with Position Reporting
- Tools such as
jsonlint,jq ., or online validators will point to the line and column where the parser first fails. - Pay special attention to the character reported as “unexpected”; it is often the first character after the point where a key was expected.
- Tools such as
-
Check for Non‑Double‑Quote String Delimiters
- Search the payload for
'(single quote) and`(backtick). Replace any occurrences with"if they are meant to delimit strings. - If the data originates from a language that permits unquoted keys (e.g., Python dicts, YAML), convert it to proper JSON before parsing.
- Search the payload for
-
Look for Trailing Commas
- Regular expression
,\s*[}\]will match a comma directly followed by a closing brace or bracket. Remove those commas.
- Regular expression
-
Inspect for Invisible Characters
- Copy the suspect string into a hex editor or run
od -c/xxdto see byte values. - Remove any bytes < 0x20 (space) that are not
\t,\n,\r, or valid escape sequences inside strings.
- Copy the suspect string into a hex editor or run
-
Verify Encoding
- If you control the source, enforce UTF‑8 without a BOM.
- When reading from a file in Python, use
open(..., encoding='utf-8'). In Node.js,fs.readFile(path, 'utf8').
-
Test Incrementally
- If the payload is large, binary‑search: split the string in half, parse each half, and narrow down to the offending segment.
- This technique quickly isolates a malformed key or stray character in multi‑megabyte logs.
-
Automate Validation in CI/CD
- Add a lint step that runs
jsonlint -qon every configuration file,
- Add a lint step that runs
