JSON Patch

How it works

A patch is an array, and its operations run in order. Each operation sees the result of the preceding operation. A failed test, missing member, invalid index or unsupported operation stops the patch. No partial patched file is offered after failure, and editing either input removes the previous result. The error identifies the one-based operation number; syntax and document errors are identified separately.

The path and from fields use JSON Pointer strings. An empty string selects the whole document, / selects a property whose name is empty, ~1 means a slash inside a name and ~0 means a tilde. URI fragments beginning with # and JSONPath expressions are not accepted. An array index must be a nonnegative integer without leading zeros. The - append marker is accepted only as an add destination, including the add part of move or copy.

Add replaces an existing object member or inserts into an array. Replace and remove require an existing target. Copy clones a value rather than linking two mutable objects. Move removes the source before resolving the destination, which matters when moving within one array. Moving a value into one of its descendants is rejected; moving to the same path leaves the value intact. Test uses JSON logical equality: object member order does not matter, array order does, and numeric spellings such as 1, 1.0 and 1e0 compare equally.

The parser keeps numeric tokens instead of round-tripping them through JavaScript Number. An ID such as 9007199254740993 therefore remains exact, and unchanged numeric spellings survive the output. Arithmetic is not performed. Number tokens longer than 4,096 characters are rejected. Strings and object names may be re-escaped and whitespace is compacted; this is value preservation rather than byte-for-byte source preservation. Duplicate object names are rejected as ambiguous, including names with different escape spellings that decode identically. Special names such as __proto__ are safely represented as Map entries and treated only as document data.

Removing the document root is deliberately rejected because it leaves no JSON document to download. Use root replace or add with null only when null is the result you actually intend. Unrecognized operation members are ignored as required by RFC 6902; an unknown operation name is an error. The tool does not fetch references, execute values, save documents in browser storage or contact an API.

Each input is limited to 256 KiB, with depth 64 and 20,000 parser tokens. A patch has at most 100 operations; pointers have at most 4,096 characters. After every operation, the result is bounded to 20,000 values, depth 64 and 512 KiB. A worker is stopped after 10 seconds, including startup; Cancel or changing an input terminates it. A timeout supplies no conclusion about whether the patch would succeed.

The patched JSON contains the complete supplied data. The separate report includes operation types, counts and output size, but omits values, paths and source filenames. Review both files before sharing. Local processing does not mean every network request made by the surrounding website is absent; it means the input documents are not uploaded by this tool.

Common use cases

• Trying a guarded API update against a local fixture before sending it
• Replaying a recorded JSON Patch while checking the failing operation
• Changing nested configuration values without rounding numeric identifiers
• Testing array move and escaped-pointer behavior with a small reproducible example

Frequently asked questions

Standards and limitations

• RFC 6902: JSON Patch operations and error handling
• RFC 6901: JSON Pointer syntax
• RFC 8259: JSON objects and number interoperability