Issues

• UBJSON/BJData high-precision numbers accept a NUL-terminated prefix inside their payload

  aspect: binary formatssolution: proposed fix
  nlohmann/json#5753 · Filter by author fhgffy opened on Oct 3, 2026 · Release 3.13.0
  2

  

• Packaging metadata: incomplete json.tar.xz and Bazel singleheader target, SwiftPM docs, REUSE dep5, stale README compiler list and CITATION.cff

  CICMakedocumentationkind: enhancement/improvement
  nlohmann/json#5716 · Filter by author nlohmann opened on Sep 30, 2026
  

• sax_parse cannot read CBOR that contains tags, including binary values with a subtype written by to_cbor

  aspect: binary formatskind: enhancement/improvement
  nlohmann/json#5676 · Filter by author nlohmann opened on Sep 29, 2026
  1

• JSON_BRACE_INIT_COPY_SEMANTICS: json j{arr} turns an array like ["key", 42] into an object

  kind: bug
  nlohmann/json#5662 · Filter by author nlohmann opened on Sep 29, 2026
  

• BJData ND-array annotations are not parsed back into the same object ("single" precision, ordered_json key order)

  aspect: binary formatskind: bug
  nlohmann/json#5661 · Filter by author nlohmann opened on Sep 29, 2026
  

• Floats are truncated at the decimal point under locales with a multi-byte decimal point (fa_IR.UTF-8)

  kind: bug
  nlohmann/json#5660 · Filter by author nlohmann opened on Sep 29, 2026
  3

  

• from_cbor()/from_msgpack() do not validate UTF-8 in text strings at decode time (only dump() does)

  aspect: binary formatskind: bugsolution: proposed fixstate: please discuss
  nlohmann/json#5529 · Filter by author nlohmann opened on Sep 15, 2026 · Release 3.13.0
  6

• Test suite: reduce runtime — 52 % is Unicode byte sweeps, plus redundant re-parsing in binary roundtrip tests

  solution: proposed fix
  nlohmann/json#5418 · Filter by author nlohmann opened on Aug 26, 2026
  1

  

• std::hash<basic_json> is inconsistent with operator== for equal cross-type numbers (breaks unordered containers)

  kind: bugsolution: proposed fix
  nlohmann/json#5400 · Filter by author nlohmann opened on Aug 25, 2026

• Stack overflow in binary format writers (CBOR/MessagePack/UBJSON/BSON) due to unbounded recursion

  nlohmann/json#5392 · Filter by author nlohmann opened on Aug 21, 2026
  2

  

• Behavior differences in operator[] object creation with a json_pointer

  state: please discuss
  nlohmann/json#5357 · Filter by author nlohmann opened on Aug 3, 2026
  1

• to_cbor()/to_msgpack() allocate a temporary basic_json for every object key

  aspect: binary formatsgood first issuekind: enhancement/improvement
  nlohmann/json#5318 · Filter by author nlohmann opened on Jul 27, 2026
  2

  

• CBOR: nested indefinite-length strings/byte strings are accepted (RFC 8949 3.2.3 requires definite-length chunks)

  aspect: binary formatsgood first issue
  nlohmann/json#5317 · Filter by author nlohmann opened on Jul 27, 2026
  1

  

• CBOR: cbor_tag_handler_t::store rejects documents that ignore accepts, and drops tag numbers 6-20

  aspect: binary formatsstate: please discuss
  nlohmann/json#5316 · Filter by author nlohmann opened on Jul 27, 2026
  1

• Idea: arena / PMR document mode (O(1) teardown, allocation-free destruction)

  nlohmann/json#5298 · Filter by author nlohmann opened on Jul 22, 2026
  5

• Idea: canonical / deterministic serialization (RFC 8785 JCS)

  nlohmann/json#5297 · Filter by author nlohmann opened on Jul 22, 2026
  1

• Idea: lossless number round-tripping (raw / arbitrary-precision number mode)

  nlohmann/json#5296 · Filter by author nlohmann opened on Jul 22, 2026

• Idea: borrowed / zero-copy read-only view over a source buffer

  nlohmann/json#5295 · Filter by author nlohmann opened on Jul 22, 2026
  

• Ideas: exploring ways to reduce compilation time

  nlohmann/json#5294 · Filter by author nlohmann opened on Jul 22, 2026
  7

• Int and uint compare equal but hashes do not

  confirmedkind: bugsolution: proposed fixstate: please discuss
  nlohmann/json#5256 · Filter by author Jezza2 opened on Jul 9, 2026
  4

• basic_json destructor allocates memory, violating noexcept semantics

  solution: proposed fixstate: please discuss
  nlohmann/json#5135 · Filter by author EvanBalster opened on Apr 13, 2026
  8

  

• Natvis file for version 3.12.0 does not contain a type definition for detail::json_default_base

  kind: bugsolution: proposed fix
  nlohmann/json#4972 · Filter by author sakuntalle opened on Oct 29, 2025
  11

  

• json destructor does not use the provided allocator

  kind: bugsolution: proposed fix
  nlohmann/json#4842 · Filter by author veselink1 opened on Jul 4, 2025
  2

  

• Binary formats invalid encoding for <discarded> values in arrays and objects

  aspect: binary formatssolution: proposed fix
  nlohmann/json#4714 · Filter by author nebkat opened on Apr 1, 2025
  14

  

• meson build does not install nlohmann_json*.cmake files

  good first issuekind: bugsolution: proposed fixstate: help needed
  nlohmann/json#3885 · Filter by author heitbaum opened on Dec 17, 2022
  11