fastjsonpatch

A drop-in replacement for jsonpatch (RFC 6902) with make_patch and apply written in Rust. It returns the same patches and documents as jsonpatch 1.34 and raises exceptions with the same types and messages.

pip install fastjsonpatch

import fastjsonpatch as jsonpatch      # the only line you change

src = {"name": "web", "replicas": 3, "ports": [80, 443]}
dst = {"name": "web", "replicas": 5, "ports": [80, 443, 8080]}

patch = jsonpatch.make_patch(src, dst)
patch.patch
# [{'op': 'replace', 'path': '/replicas', 'value': 5},
#  {'op': 'add', 'path': '/ports/2', 'value': 8080}]

patch.apply(src) == dst                # True; src is not modified
jsonpatch.apply_patch(src, [{"op": "remove", "path": "/ports/0"}])
# {'name': 'web', 'replicas': 3, 'ports': [443]}

Requires CPython 3.12+. Wheels are published for Linux (x86_64, aarch64; glibc and musl), macOS (arm64, x86_64) and Windows (x64). The only dependency is jsonpointer.

Performance

Linux x86_64, Python 3.13, best of several runs:

Across all measured workloads, make_patch is 9-57x faster and apply 4-27x (4x is a 3-operation patch applied in_place to a 3.8 MB document, where no copy is made). On Python 3.14, whose copy.deepcopy is faster, the apply speedup is smaller (about 6x instead of 11x on the 10k-record workload). Full tables and an explanation of where the time goes are in BENCHMARKS.md; python bench/compare.py (in the source distribution) measures on your machine.

Compatibility

fastjsonpatch is jsonpatch 1.34's module with JsonPatch.__init__ (validation), JsonPatch.from_diff (make_patch) and JsonPatch.apply (apply_patch) routed to Rust; every other public name is jsonpatch's own code. Inputs the Rust code does not handle exactly fall back to jsonpatch's original code before anything is modified: non-JSON values, dict or list subclasses, nesting deeper than 1000, a custom dumps= or json_dumper, a custom pointer_cls, operations or _get_operation (for apply), and operations that would fail.

Known differences:

• The exception classes are fastjsonpatch's own, so except fastjsonpatch.JsonPatchConflict does not catch an exception raised by the jsonpatch package, and vice versa.
• Values in a document that are not dicts, lists or JSON scalars are copied with copy.deepcopy one by one, so aliasing between such values is not preserved.
• __version__ is fastjsonpatch's version; __jsonpatch_version__ is "1.34". jsonpatch's __author__ and __website__ are not defined.

Testing

About 1,580 tests: randomized comparisons against jsonpatch 1.34 (patches, documents and errors), jsonpatch's own test suite and doctests, and the json-patch-tests RFC 6902 suite. CI runs them with Python 3.12-3.14 on Linux (x86_64, aarch64; glibc), macOS (arm64, x86_64) and Windows (x64); the musl wheels are built but not tested in CI.

License

BSD-3-Clause. The Python module and the diff algorithm come from jsonpatch (Copyright (c) 2011 Stefan Kögl, BSD). Licenses of the Rust crates compiled into the wheels are in THIRD_PARTY_LICENSES.md. Development and release notes: MAINTAINING.md.