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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false), but the description adds real behavioral value beyond them: consent remains unknown, suppressed addresses are rejected, and an existing contact with the same address is filled in rather than duplicated. It does not mention permissions or what the call returns, but for an annotated mutation tool this is solid disclosure.

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 tight sentences, zero filler, with the core create/upsert behavior front-loaded before the consent and suppression caveats.

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 mutation tool with no output schema and a nested attributes object, the description covers the behavioral edge cases an agent most needs (consent state, suppression, upsert). Missing only return-value expectations and any permission requirements, which keeps it short of full completeness.

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 80% (4 of 5 properties documented, only 'name' bare), so the schema already carries most parameter meaning. The description adds only indirect parameter insight — that no consent parameter exists here and that opt-in needs a separate action — without clarifying any parameter's format or constraints.

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?

States a specific verb and resource ('Adds one contact to a product by email') and immediately distinguishes its behavior from a plain create by noting the upsert case ('or fills in an existing contact with that address'), which separates it from update_contact and search_contacts in the sibling list.

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?

Gives clear operational context and implicit exclusions: suppressed addresses are not added, and opt-in recording 'is a separate action requiring its source' (pointing away from set_contact_consent). It stops short of explicitly naming the alternative tools or stating when a caller should prefer update_contact over this tool.

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