jsondiffview

jdv produces deterministic, JSON-shaped review text for humans. It compares strict JSON only: the first argument is the old (before) document and the second is the new (after) document.

The output is annotated review text, not valid JSON, JSON Patch, or an applyable patch. Additions (+), removals (-), modifications (~), moves (>), omissions (…), and intraline spans ([-old-], [+new+]) remain readable without color.

The package published on PyPI is named jsondiffview; the import package is also jsondiffview, while the installed CLI command is jdv.

Upgrading from 2.1.2? Read Migrating to 3.0.0. This source tree builds local 3.0.0 artifacts but does not publish them.

Install and run

For development:

uv sync
uv run jdv --help

Or build and install the local wheel:

uv build --no-sources
uv tool install ./dist/jsondiffview-3.0.0-py3-none-any.whl

Both entry points use the same implementation:

jdv before.json after.json
python -m jsondiffview before.json after.json

One input may be read from stdin:

cat before.json | jdv - after.json

Copy-ready PowerShell commands and editable sample documents are available in the playground.

Command

Usage: jdv [OPTIONS] OLD_JSON NEW_JSON

  Compare strict OLD_JSON (before) with NEW_JSON (after).

Options:
  -v, --view [summary|review|full]
                                  Detail level.  [default: review]
  -k, --match-key FIELD           Array-object identity key; repeat in
                                  priority order. Any occurrence replaces
                                  defaults: id, key, name, title.
  -c, --color [auto|always|never]
                                  Review color policy.  [default: auto]
  -q, --quiet                     Suppress the equality notice only.
  --version                       Show the version and exit.
  -h, --help                      Show this message and exit.

Option choices and match-key names are case-sensitive. Repeating --match-key preserves command-line priority and replaces all default keys; supplying the same key twice is an error. -- ends option parsing for paths that begin with -. A file literally named - is not addressable, and both arguments cannot use stdin.

Views

• review (default) expands every changed, added, and removed value and keeps one adjacent unchanged sibling around each changed run.
• summary collapses every unchanged sibling run and may summarize large wholly added or removed containers with a bounded first-two-child preview and exact omitted-descendant count.
• full expands all structural context and added/removed subtrees.

All views use the same semantic comparison. Deterministic long-string safety limits remain active even in full.

Status and stream contract

Status 1 is an expected diff-style result, not an operational failure. --quiet suppresses only the equality notice. A closed stdout pipe exits 2 without a diagnostic or traceback.

A CI-safe shell pattern is:

set +e
jdv --color never before.json after.json
status=$?
set -e
if [ "$status" -gt 1 ]; then
  exit "$status"
fi

Review format

Every physical line starts with a two-column semantic prefix. Object keys are JSON strings; array entries use new indexes such as [2]:, while unmatched removals use old indexes such as [old 4]:.

~ {
~   "services": [
      [0]: {
        "id": "api",
…       1 unchanged field omitted
      },
>     moved from $.services[2] to $.services[1] (matched by "id": "db")
      [1]: {
        "id": "db",
…       1 unchanged field omitted
      },
~     [2]: {
        "id": "worker",
~       "port": 9000 -> 9001
      }
    ],
~   "title": "Hello [-world-][+team+]",
-   "obsolete": true
  }

Modified short strings use Unicode grapheme-safe word-, whitespace-, and punctuation-segment spans. When one identifier or number segment has a useful shared prefix or suffix, finer grapheme detail is used without splitting a user-perceived character. Multiline strings are compared as exact logical lines, with line terminators visible as JSON escapes; sufficiently similar replacement lines can show side-specific intraline spans. Over-budget multiline changes retain bounded first/last previews with exact omitted line and code-point counts. Adaptive classification keeps prose inline while routing dense separators and opaque runs to bounded hunk output. Long single-line strings report Unicode code-point lengths, half-open offsets, display-cell-bounded excerpts, and exact omission counts. All matching and output limits are deterministic work counters, including in full. Strings shown only on one side or as unchanged context are also bounded at 512 code points, including values containing line breaks.

The main review above includes a pure move (db). Array removals retain their old index:

~ [
    [0]: "keep",
-   [old 1]: "gone"
  ]

A moved entry can also contain a nested modification:

~ [
>   moved from $[1] to $[0] (matched by "id": "b")
~   [0]: {
      "id": "b",
~     "v": 1 -> 2
    },
    [1]: {
      "id": "a",
…     1 unchanged field omitted
    }
  ]

Ambiguous identity values remain explicit additions and removals:

~ [
+   [0]: {
+     "id": "x",
+     "v": 3
+   },
+   [1]: {
+     "id": "x",
+     "v": 4
+   },
-   [old 0]: {
-     "id": "x",
-     "v": 1
-   },
-   [old 1]: {
-     "id": "x",
-     "v": 2
-   }
  ]

Color is presentation only: yellow marks modifications, red removals, green additions, and cyan move provenance. --color auto requires a terminal and an absent or empty NO_COLOR; always overrides both redirection and NO_COLOR; never disables ANSI. FORCE_COLOR is intentionally ignored.

Strict JSON and matching

Inputs use RFC JSON syntax with unique object names and project-owned numeric limits:

• UTF-8 and an optional leading UTF-8 BOM are accepted.
• Duplicate object keys, NaN, Infinity, and -Infinity are rejected.
• Integer literals are limited to 4,300 digits.
• Decimal/exponent lexemes are limited to 10,000 code points.
• Container nesting is limited to 256 levels; there is no global file-size limit.
• A decimal/exponent value whose binary64 conversion is non-finite, such as 1e999, is rejected.
• Integer 1, decimal/exponent 1.0, boolean true, and string "1" are distinct. Decimal spellings 1.0 and 1.00 compare equal.
• Object member order is ignored; array order matters.

Array entries are never paired by position or fuzzy similarity. Object entries pair only when a configured identity value is unique on both sides. The defaults are id, key, name, and title; use -k FIELD to replace them. Remaining globally unique entries pair by exact strict value. Repeated exact values may align monotonically to stabilize the review, but that alignment is not identity evidence and never fabricates a move. Other ambiguous values remain a removal plus an addition. Null, object, and array identity-key values are unavailable, and a lower-priority key cannot override conflicting higher-priority scalar identities.

Moves are the minimal deterministic relative-order changes among matched entries. Insertions and removals that merely shift absolute indexes do not mark every survivor as moved. A moved entry keeps its old/new paths and can also show nested modifications.

Development

uv sync --locked --group dev
uv run --locked pytest -q
uv run --locked ruff check .
uv run --locked ruff format --check .
uv run --locked mypy src tests
uv run --locked python -m jsondiffview --help
uv run --locked jdv --version
uv build --no-sources

The package supports CPython 3.11 and newer.