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Rule Reference

SEC318lintai-ai-securitycompatqualitystabletool_jsonwarn

Anthropic strict schema: missing additionalProperties false

Anthropic strict tool input schema omits additionalProperties: false

Public lane
compat
Category
quality
Provider
lintai-ai-security
Scope
per-file
Surface
tool_json
Tier
stable
Severity
warn
Confidence
high
Detection
structural
Remediation
message only
How to read this lane

Config, schema, and policy contract review.

How to read this category

Contract, schema, or config correctness signal.

Activation Model

Preset Activation

These presets explain where this rule appears in the product experience.

compatsidecar lane
mcpsurface preset

Lifecycle

Stable Lifecycle Contract

State

stable

Graduation rationale

Checks Anthropic strict tool input_schema objects for explicit additionalProperties: false.

Deterministic signal basis

ToolJsonSignals recursive schema walk over Anthropic input_schema when strict mode is enabled.

Malicious corpus
tool-json-anthropic-strict-open-schema
Benign corpus
tool-json-anthropic-strict-locked
structured evidence required remediation reviewed
Canonical note

Structural stable rule intended as a high-precision check with deterministic evidence.

Nearby Signals

Related Rules

SEC314Tool descriptor: missing machine fieldsMCP-style tool descriptor is missing required machine fieldscompatqualitytool_json
SEC315Tool descriptors: duplicate tool namesMCP-style tool descriptor collection contains duplicate tool namescompatqualitytool_json
SEC316OpenAI strict schema: missing additionalProperties falseOpenAI strict tool schema omits recursive additionalProperties: falsecompatqualitytool_json
SEC317OpenAI strict schema: properties not all requiredOpenAI strict tool schema does not require every declared propertycompatqualitytool_json

Why It Matters ​

Anthropic strict tool schemas are meant to be locked down. If input_schema leaves object nodes open, the declared contract is less deterministic than it appears.

What Triggers ​

SEC318 applies to Anthropic-style strict tool definitions and triggers when input_schema omits additionalProperties: false on object nodes.

Example that triggers:

json
[
  {
    "name": "weather",
    "strict": true,
    "input_schema": {
      "type": "object",
      "properties": { "city": { "type": "string" } },
      "required": ["city"]
    }
  }
]

False Positives ​

This is a structural schema-locking rule over parsed Anthropic-style tool descriptors.

Remediation ​

Lock the strict input_schema with additionalProperties: false on every object node.