Which JSON Schema draft is supported?

ajv 8.x default — draft-07, the most widely compatible. The 2020-12 draft (prefixItems, unevaluatedProperties, …) requires the ajv/dist/2020 build — that becomes a V2 option.

What about validateFormats?

Disabled. The tool runs without ajv-formats — string formats like `format: "email"` or `format: "uuid"` are ignored. If format checking matters, V2 may add ajv-formats. All other keywords (type, required, pattern, enum, minimum, ...) work normally.

Which JSONPath dialect?

jsonpath-plus superset. Basics: $.store.books[*].title. Filters: $..books[?(@.price < 10)]. Recursion: $..author. Slices: $..books[0:2]. Close to RFC 9535.

Is it fast on large JSON?

Up to ~10MB runs comfortably on the main thread. ajv recompiles when the schema changes; JSONPath re-evaluates on path change. A 150ms debounce absorbs typing bursts. Above ~100MB the browser may run into memory limits.

Can I trust the validation in production?

ajv is the standard JSON Schema validator, so the verdict is reliable. The schema's own correctness is a separate question — this tool can't tell whether your schema *means* the right thing (missing required, wrong type, etc.). That's a code review.

JSON Schema validator + JSONPath extractor · ajv validation · JSONPath query

When to use it

Confirming an API response satisfies a schema spec right before integration testing, pulling specific fields out of a large JSON for debugging, or simulating what the frontend will receive after a backend schema change to spot what breaks.

Two modes, one tool

Toggle from the top:

Schema validation — JSON Schema (draft-07) validates your data. Every violation surfaces at once (allErrors). Three columns: instance path, keyword, message.
JSONPath extraction — pulls only the matching nodes from a large JSON via a path expression. jsonpath-plus superset syntax.

They're orthogonal — schema is whole-document validation, JSONPath is partial extraction. Both come up often enough that bouncing between sites for them is annoying — one tool, both modes.

Lazy libraries

ajv 8.x (~80KB gz) — the de-facto JSON Schema validator.
jsonpath-plus 10.x (~5KB gz) — JSONPath evaluator.

Both dynamically imported. The page's client bundle stays ~10KB; ajv / jsonpath-plus chunks load when you start typing.

JSONPath cheatsheet

$.store.books[*].title         # all book titles
$..books[?(@.price < 10)]      # books cheaper than 10
$..author                      # all author keys (recursive)
$..books[0:2]                  # first two books
$..books[-1:]                  # last book
$.store.books[*].price         # all prices

Close to RFC 9535, but jsonpath-plus is a slight superset (script expressions like ?(@...) extend the standard).

Schema-mode keywords

The full ajv 8.x draft-07 set:

type (string, number, integer, boolean, object, array, null)
required, enum, const
properties, additionalProperties, patternProperties
items, minItems, maxItems, uniqueItems
pattern, minLength, maxLength
minimum, maximum, exclusiveMinimum, exclusiveMaximum
multipleOf
if / then / else, allOf / anyOf / oneOf / not

format (email, uuid, date-time, …) is ignored in V1 (no ajv-formats). Add it in V2 if format checking matters.

Not the right tool when

API mocking / fake server — generating fake data that satisfies a schema is separate. This tool validates only; it doesn't generate. Use faker / json-schema-faker for that.
Reviewing the schema's design — missing required, wrong types, and other schema design problems are not detected automatically. This tool checks only formal correctness.
OpenAPI / Swagger directly — paste the embedded component schema by hand. This tool takes raw JSON Schema only.

Privacy

Auth tokens, user IDs, and payment fields embedded in API responses are safe. ajv and jsonpath-plus are dynamically imported into the client bundle; the schema, data, and path never leave the page.

JSON stays on the page