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

Annotations already declare destructiveHint=true, idempotentHint=false and openWorldHint=true, so the safety bar is lower; the description still earns credit by disclosing the duplicate-mobile merge behavior and the important caveat that "a contact is not opted in to messages by this call." It omits permissions/auth requirements and what the call returns, keeping it below a 5.

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-loaded with the write operation and immediately followed by the riskiest edge case (duplicate mobile merge). No filler.

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?

With no output schema, an agent still knows the key semantics: it is a write, duplicate mobiles are merged per merge_strategy, and no opt-in occurs. Missing return-value shape (e.g. created contact id) and auth requirements are the only notable gaps for a 6-param mutation tool.

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 50%, so the description should compensate somewhat; it mentions merge_strategy but only restates the enum values ("append, core or remove, per Sakari") without explaining what each mode actually does to the existing contact. email, first_name and last_name get no mention in either place.

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 ("WRITE: create a contact") and adds the duplicate-mobile condition that qualifies the operation. It doesn't name the sibling sakari_update_contact as the alternative for modifying an existing contact, so differentiation is only implicit.

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?

"If a contact with the same mobile number exists, merge_strategy decides what happens" gives useful context about when merging applies, and it clarifies this is not an opt-in action. However, there is no explicit when-to-use/when-not guidance and no routing to sakari_update_contact or sakari_get_contact for the modify/check paths.

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