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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuine payload context beyond that: entries vary in shape (name absent for unsaved contacts) and the absence of a blocked-date is explained by WhatsApp behavior rather than left as a mystery. This is useful disclosure, though pagination or result-size behavior is not addressed.

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 sentences, front-loaded with the action and scope, then the entry shape. Every sentence carries some information, though the country/name detail could be trimmed since an output schema exists. No wasted preamble.

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 simple read-only list with an output schema and full parameter documentation, the description supplies the extra behavioral nuances (missing name, no block date) an agent would otherwise infer wrongly. Little is missing beyond pagination behavior on large blocklists.

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% and the single account_id parameter is documented in the schema with a pointer to wa_list_accounts. The description adds no further parameter meaning, so the baseline 3 applies.

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 and resource: 'List every contact one of your accounts has blocked.' This clearly separates it from the write-side sibling wa_block_contact and from the general wa_list_contacts. It stops short of explicitly naming those siblings, so it is clear but not fully self-differentiating.

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?

Usage is implied by the blocklist scoping ('one of your accounts has blocked'), but there is no explicit when-to-use guidance, no mention of how it differs from wa_list_contacts, and no pointer to wa_block_contact for the write path. Adequate but leaves routing to inference.

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