Empty string passed to a JSON parser

The document is zero bytes. Almost always an upstream failure: an HTTP call that returned 204, a file that was never written, a variable that was never assigned, or a response body already consumed by an earlier read.

Reproduce it

The input

Fails to parse

Parses correctly

{}

Open this broken input in the formatter →

The fix

How to fix it

Check for an empty body before parsing, and log the status code and content-length alongside it.

An empty body with a 200 status usually means the response stream was read twice. The second read returns nothing.

Cross-runtime

What each parser reports

Every message below was captured by running this exact input through the parser named. 15 of 21 parsers rejected it; 6 accepted it.

Parser	Exact message
CPython json.loads CPython 3.12.3	`Expecting value: line 1 column 1 (char 0)` what this message means →
encoding/json Unmarshal Go go1.22.2	`unexpected end of JSON input` what this message means →
Gson Java 21.0.12	accepted — no error
Gson JsonParser (lenient off) Java 21.0.12	accepted — no error
hjson Node.js 22.22.2	accepted — no error
Jackson ObjectMapper Java 21.0.12	accepted — no error
JavaScriptCore JSON.parse JavaScriptCore (Bun 1.4.1)	`JSON Parse error: Unexpected EOF` what this message means →
json-bigint Node.js 22.22.2	`Unexpected ''`
JSON5 Node.js 22.22.2	`JSON5: invalid end of input at 1:1` what this message means →
JSON::PP Perl 5.038002	`malformed JSON string, neither array, object, number, string or atom, at character offset 0 (before "(end of string)")` what this message means →
json_decode PHP 8.3.6	`Syntax error`
Newtonsoft.Json JsonConvert Newtonsoft.Json 13.0.3 on .NET 8.0.30	accepted — no error
Newtonsoft.Json JsonTextReader Newtonsoft.Json 13.0.3 on .NET 8.0.30	accepted — no error
orjson CPython 3.12.3	`Input is a zero-length, empty document: line 1 column 1 (char 0)` what this message means →
Ruby JSON.parse Ruby 3.2.3	`unexpected token at ''`
serde_json::from_str Rust (serde_json 1.x)	`EOF while parsing a value at line 1 column 0` what this message means →
SpiderMonkey JSON.parse SpiderMonkey 115	`JSON.parse: unexpected end of data at line 1 column 1 of the JSON data` what this message means →
System.Text.Json Deserialize .NET 8.0.30	`The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. Path: $ \| LineNumber: 0 \| BytePositionInLine: 0.` what this message means →
System.Text.Json JsonDocument .NET 8.0.30	`The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. LineNumber: 0 \| BytePositionInLine: 0.` what this message means →
ujson CPython 3.12.3	`Expected object or value`
V8 JSON.parse Node.js 22.22.2	`Unexpected end of JSON input` what this message means →

Standards

What the specification says

The exact sections that govern this error. Descriptions are our paraphrase; follow the links for the normative text.

Body	Section
IETF	RFC 8259 (STD 90) §2 — JSON Grammar A JSON text is a single value with optional surrounding whitespace (`JSON-text = ws value ws`). The token set is six structural characters, strings, numbers and three literal names — nothing else.
Ecma International	ECMA-404, 2nd edition §4 JSON Text Lists the six structural tokens, the three literal name tokens, and the four whitespace code points. Whitespace is not allowed within a token.

Empty string passed to a JSON parser

The input

How to fix it

What each parser reports

What the specification says

Other errors in this category

Whitespace-only input

Extra data after a JSON document

Trailing characters after a JSON document

HTML received where JSON was expected

The literal string 'undefined' as a JSON document

Bare unquoted word as a JSON document

Whole JSON document wrapped in quotes

NDJSON fed to a whole-document JSON parser