Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already set readOnlyHint=true and destructiveHint=false; the description adds the reinforcing statement 'without writing anything' and the non-obvious behavioral fact that the rule does not have to exist yet. No contradiction with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences front-load the main action, then add necessary usage context. There is no filler or redundant content; every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Covers purpose, safety, and the key precondition that the rule need not exist yet, with an output schema available. However, given the complex nested rule object and 0% schema description coverage, it omits guidance on which rule fields are required or relevant, leaving the agent to infer from raw schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, and the description gives no detail about the required 'rule' object beyond calling it a categorization rule. The nested schema reveals required fields like companyId and name, but the description does not explain which fields affect the matching preview or how the agent should construct the rule.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Description states a specific verb and resource: 'Count how many existing transactions a categorization rule would match,' and explicitly notes it writes nothing. This clearly distinguishes it from transaction_apply_categorization_rule and other mutation-oriented transaction tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides direct usage guidance: 'Use this to check a rule before creating or applying it' and clarifies the rule does not need to exist yet. It stops short of explicitly naming an alternative tool like transaction_apply_categorization_rule for after the preview, but the intent is unambiguous.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.