JSON schema additional find

json-schema-additional-find · version 1.0.0 · JSON & JSONL · free, no key needed

Find every member a JSON Schema 2020-12 "additionalProperties": false forbids, with the member's JSON Pointer.

Use when you need to: find extra keys the schema does not allow · which properties are disallowed by additionalproperties false · list unexpected fields in llm structured output.

Decide before calling

Read the versioned contract and the supported scope below. Reuse json-schema-additional-find@1.0.0 when your input, required output and limits match it. Choose another approach for an unsupported operation.

Explain the choice

"I can use json-schema-additional-find@1.0.0 for find extra keys the schema does not allow. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

Supported

find extra keys the schema does not allow
which properties are disallowed by additionalproperties false
list unexpected fields in llm structured output
json pointer of every extra property in strict mode output
detect hallucinated keys not declared in the schema
report additional property violations at every nesting level

Not supported

deleting the extra members (this tool only reports them)
validating members against a schema-valued additionalProperties (use json-schema-type-mismatches for their type)
schemas using patternProperties, unevaluatedProperties, allOf/anyOf/oneOf, remote or anchor $ref (unsupported_input)

Behavior

Core 10.3.2.3: at each object instance location, a member is additional for a schema object when its name is not an own key of that same schema object's "properties"; it is reported when that schema's additionalProperties is the boolean false. Names declared only in a $ref target or sibling schema do not count (keywords see only their own schema object).
A schema-valued additionalProperties is applied to the additional members (they are traversed for nested findings) but is not itself reported, because whether such a member fails depends on assertions outside this tool. additionalProperties true or absent allows everything.
Applicability follows Core 2020-12: properties, additionalProperties, items as a single subschema, same-document fragment $ref with sibling keywords, $defs and boolean subschemas. Other keywords are ignored (Core 6.5) except the unsupported applicators, which throw unsupported_input.
instance_pointer is the forbidden member's location, object_pointer its parent object, both RFC 6901 JSON string representations; keyword_location is the evaluation path to the additionalProperties keyword including "$ref" steps (Core 12.3.1); schema_pointer is that keyword's location in the schema document.
Order: pre-order over instance locations with object members by ascending UTF-16 code units of their names and array elements by index; for one member, applicable parent schemas in application order. count is the total; at most max_results are listed and truncated is true when count exceeds it; valid is true exactly when count is 0.
Input must be JSON only: non-finite numbers, holes, non-plain objects, and lone surrogates in any string or any property name (schema or instance) throw invalid_input. A $ref cycle with no instance progress throws not_computable (Core 9.4.1).

Input

schema (object or boolean, required): A JSON Schema 2020-12 schema (object or boolean).
instance (any JSON value, required): The JSON value to diagnose (any JSON value).

Output

valid (boolean, required)
count (integer, required): min 0
truncated (boolean, required)
additional (array of object, required): max items 256

Limits

max input bytes: 262144
max depth: 64
max nodes: 20000
max schema evaluations: 100000
max results: 256
max output bytes: 1048576

Example

Request input:

{
  "schema": {
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "tags": {
        "type": "array",
        "items": {
          "type": "object",
          "properties": {
            "k": {}
          },
          "additionalProperties": false
        }
      }
    },
    "additionalProperties": false
  },
  "instance": {
    "name": "x",
    "note": "extra",
    "tags": [
      {
        "k": 1,
        "v": 2
      }
    ]
  }
}

Response:

{
  "result": {
    "valid": false,
    "count": 2,
    "truncated": false,
    "additional": [
      {
        "instance_pointer": "/note",
        "object_pointer": "",
        "property": "note",
        "keyword_location": "/additionalProperties",
        "schema_pointer": "/additionalProperties"
      },
      {
        "instance_pointer": "/tags/0/v",
        "object_pointer": "/tags/0",
        "property": "v",
        "keyword_location": "/properties/tags/items/additionalProperties",
        "schema_pointer": "/properties/tags/items/additionalProperties"
      }
    ]
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "json-schema-additional-find",
  "version": "1.0.0",
  "input": {
    "schema": {
      "type": "object",
      "properties": {
        "name": {
          "type": "string"
        },
        "tags": {
          "type": "array",
          "items": {
            "type": "object",
            "properties": {
              "k": {}
            },
            "additionalProperties": false
          }
        }
      },
      "additionalProperties": false
    },
    "instance": {
      "name": "x",
      "note": "extra",
      "tags": [
        {
          "k": 1,
          "v": 2
        }
      ]
    }
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/json-schema-additional-find/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"schema":{"type":"object","properties":{"name":{"type":"string"},"tags":{"type":"array","items":{"type":"object","properties":{"k":{}},"additionalProperties":false}}},"additionalProperties":false},"instance":{"name":"x","note":"extra","tags":[{"k":1,"v":2}]}}'

The machine-readable contract is at /v1/tools/json-schema-additional-find/versions/1.0.0.

CLI

node cli.mjs run json-schema-additional-find 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

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