require-tool-schema

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Ensures all AI tools have Zod schema validation for input parameters.

Get weather

📊 Rule Details

Property	Value
Type	suggestion
Severity	🟡 HIGH
OWASP Agentic	ASI02: Tool Misuse & Exploitation
CWE	CWE-20: Improper Input Validation
CVSS	7.0
Config Default	`warn` (recommended), `error` (strict)

🔍 What This Rule Detects

This rule identifies AI tools that lack input schema validation. Without schema validation, AI models can pass arbitrary data to tool execute functions, enabling exploitation.

❌ Incorrect Code

// No schema
const tools = {
  weather: {
    execute: async (params) => getWeather(params.location),
  },
};

// Missing inputSchema in tool() helper
const myTool = tool({
  description: 'Get weather',
  execute: async (params) => getWeather(params.location),
});

✅ Correct Code

// With inputSchema
const tools = {
  weather: {
    inputSchema: z.object({
      location: z.string().max(100),
    }),
    execute: async ({ location }) => getWeather(location),
  },
};

// Using tool() helper with schema
const weatherTool = tool({
  description: 'Get weather',
  inputSchema: z.object({
    location: z.string().max(100),
    unit: z.enum(['celsius', 'fahrenheit']).optional(),
  }),
  execute: async ({ location, unit }) => getWeather(location, unit),
});

⚙️ Options

Option	Type	Default	Description
`schemaPropertyNames`	`string[]`	`['inputSchema', 'parameters', 'schema']`	Property names considered as valid schemas

🛡️ Why This Matters

Without input validation, AI agents can:

Pass malicious data - Inject SQL, paths, or commands
Bypass business logic - Skip validation rules
Cause DoS - Pass extremely large or nested data
Exploit type confusion - Pass unexpected data types

require-tool-confirmation - Require confirmation for destructive tools
require-output-filtering - Filter tool output

Known False Negatives

The following patterns are not detected due to static analysis limitations:

Schema from Variable

Why: Schema stored in variables is not analyzed.

// ❌ NOT DETECTED - Schema from variable
const schema = z.object({ location: z.string() });
const tools = { weather: { inputSchema: schema, execute: fn } };

Mitigation: Define schemas inline in tool definitions.

Dynamic Tool Definitions

Why: Dynamically created tools are not checked.

// ❌ NOT DETECTED - Dynamic tool creation
const tools = createTools(toolConfigs); // May not have schemas

Mitigation: Apply rule to tool factory functions.

Weak Schema Validation

Why: Schema quality is not assessed.

// ❌ NOT DETECTED - Overly permissive schema
const tools = {
  execute: {
    inputSchema: z.object({}).passthrough(), // Allows any extra fields!
    execute: fn,
  },
};

Mitigation: Use strict schemas. Avoid .passthrough().

Tool Helper Wrappers

Why: Custom tool helpers may not be recognized.

// ❌ NOT DETECTED - Custom helper
const weatherTool = createTool({
  name: 'weather',
  handler: getWeather, // No schema visible
});

Mitigation: Configure schemaPropertyNames for custom helpers.

📚 References

Error Message Format

The rule provides LLM-optimized error messages (Compact 2-line format) with actionable security guidance:

🔒 CWE-20 OWASP:A06 CVSS:7.5 | Improper Input Validation detected | HIGH [SOC2,PCI-DSS,HIPAA,GDPR,ISO27001]
   Fix: Review and apply the recommended fix | https://owasp.org/Top10/A06_2021/

Message Components

Component	Purpose	Example
Risk Standards	Security benchmarks	CWE-20 OWASP:A06 CVSS:7.5
Issue Description	Specific vulnerability	`Improper Input Validation detected`
Severity & Compliance	Impact assessment	`HIGH [SOC2,PCI-DSS,HIPAA,GDPR,ISO27001]`
Fix Instruction	Actionable remediation	`Follow the remediation steps below`
Technical Truth	Official reference	OWASP Top 10

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