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

Annotations already declare destructiveHint=true, so the mutation nature is covered. The description ADDS the key behavioral traits beyond annotations: requires email confirmation via a URL valid for 7 days, and the idempotency semantics (re-using key returns original subscription). These are valuable additions that annotations don't convey. Note: annotations say idempotentHint=true, and the description confirms idempotency — consistent.

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?

Two sentences, zero wasted words. Front-loads the core action, then covers the two critical call-enabling behaviors: confirmation URL requirement and idempotency. 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?

For a subscription tool with no output schema, the description covers the essential flow: subscribe → get confirmation URL → click within 7 days. The idempotency behavior is documented. It doesn't describe the output/return format in detail, but there's no output schema and the core semantics are adequately conveyed. Mostly complete.

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 coverage is 100%, so baseline is 3. The description adds value by clarifying that contact_email is 'confirmed via returned token' and that topics are 'topic tags' with examples. The idempotency_key semantics are well explained in the description ('re-using same key returns original subscription'). This goes beyond the schema's minimal 'Idempotency key' label.

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 states a specific verb+resource: 'Subscribe a user's email to updates from a business.' It clearly distinguishes this from siblings (search_businesses, get_quote, etc.), which are read/query operations. Loses a point because it doesn't explicitly differentiate this subscription tool from query_business_agent or request_callback, which could also be interpreted as engagement 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?

The description gives clear context (subscribe business updates, confirmation URL, 7-day validity, idempotency behavior). However, it doesn't explicitly state when NOT to use this tool or name an alternative. The 7-day confirmation constraint and idempotency note provide good operational context.

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