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

No annotations are provided, so the description must disclose side effects. It only says 'update' which implies mutation but does not clarify whether unspecified fields are preserved or reset when only some parameters are passed, nor explain return values or error behavior. This is a significant gap for a mutation tool.

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?

A single, front-loaded sentence that communicates purpose and scope efficiently without wasteful words. It even uses parentheses to enumerate key options.

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?

For a tool with 6 optional parameters, nested objects, and no output schema, the description is too terse. It fails to explain partial update semantics, behavior on invalid rule_id, or what the API returns. Given the complexity and lack of annotation support, this is incomplete.

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?

The schema covers 100% of parameters, so baseline is 3. The description adds a concise overview of which parameters are involved ('match/actions/priority') but does not add syntax, validation rules, or interactions beyond what the schema already states.

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?

The description clearly states the verb 'Update' and the resource 'existing email rule', then enumerates the changeable aspects: 'enable/disable, change match/actions/priority'. This distinguishes it from sibling tools like create_email_rule and delete_email_rule.

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?

The phrase 'existing email rule' implies this is for modifying already-created rules, distinguishing it from create/delete alternatives. It provides clear context but does not explicitly state when not to use it or name alternatives.

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