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

Annotations only say destructiveHint=true and openWorldHint=true; the description goes well beyond that by disclosing that upsert overwrites an existing active member's fields, that an unsubscribed member is re-activated unless suppress_reactivation is set, and that a confirmation email is sent on double opt-in lists. That is exactly the consequence-level detail an agent needs before calling a mutation.

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?

Four short sentences, front-loaded with the WRITE marker and the core action, then layering opt-in, consent and upsert semantics. No filler and no restatement of the title.

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 an 8-parameter destructive mutation with no output schema, it covers the consent precondition, confirmation-email behavior and the upsert/reactivation consequences. It is a bit thin on the required ip/source_url provenance fields and on failure modes beyond the default upsert error.

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 88%, so baseline is 3, but the description adds relational meaning the schema cannot: the interaction between upsert and suppress_reactivation and the overwrite consequence. It still says nothing about ip, source_url or custom_fields, which the schema carries alone.

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?

Opens with 'WRITE: add one email address to a mailing list (subscribe)' — a specific verb, resource and cardinality ('one email address'). That framing separates it cleanly from laposta_update_member and laposta_list_members without needing to name them.

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 real conditions for use: double opt-in lists trigger a confirmation email, and 'the address must have given consent' sets a precondition. It also explains when upsert applies, though it never explicitly names laposta_update_member as the alternative for editing an existing member.

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