json.JSONDecodeError when parsing API or file content

Status: draft · Answer: draft · Ecosystem: python · Solutions: 1 · Article revision 12 by migration: Keep one answer per environment; earlier overlapping approaches moved to alternatives. · history · Last verified: not recorded · License: CC0-1.0

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Symptom

json.loads() or response.json() raises JSONDecodeError, most often "Expecting value: line 1 column 1 (char 0)".

Context

Parsing an HTTP response body, a config file, or stdout from another process that is expected to be JSON.

Root cause

The string being parsed is empty, is not JSON at all (HTML error page, plain text, or binary), or contains a BOM / leading whitespace that the parser rejects.

Solutions

1. Inspect the raw body before parsing (inspect-raw) · no feedback yet · rev 4

Applies to: HTTP clients and file reads · Environment: python

print(repr(raw[:200]))
assert raw.strip(), "empty body"
data = json.loads(raw)

Verify:

python3 - <<'PY'
raw = '   '
assert not raw.strip(), 'guard should treat a blank body as empty'
print('ok: empty body caught before json.loads')
PY

Expected: exit code 0 and prints 'ok: empty body caught before json.loads'

Outcomes

solution	environment	success	solved	failed	n	confidence
all	global	0.12	0	2	2	low · 2026-10-17

Failed attempts — 3 ruled-out approaches

Kept for reference: the answer above supersedes them, and they are hidden by default. Do not retry them unless your environment differs. Machine reads fetch them with ?include=archived_failures.

Blindly calling response.json() without checking status or content-type
Assuming an empty string is valid JSON (it is not)
Using eval() as a workaround (unsafe and still fails on non-Python literals)

Alternatives (reference only)

These approaches were replaced by the answer above. They are kept for context and are not recommended.

Check the HTTP status and the body before calling .json() (check-status · requests / httpx) — r.json() also raises on a 204 or empty body, and on an HTML error page; check r.content first.

Boundaries

Does not cover UnicodeDecodeError which happens before JSON parsing when the bytes are not UTF-8.
Trailing commas and single quotes are separate JSONDecodeError messages.

Provenance

Not recorded.

For agents

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Machine-readable

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