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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, and the description adds meaningful context on top: auth requirement, exact return payload (thread, full public messages, next_page_token), and concrete failure modes (404 thread_not_found, invalid_page_token). It also flags message text as untrusted data, which annotations cannot convey.

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?

Everything is packed into a single dense paragraph with usage leading and error cases trailing, so it is well front-loaded and nearly every clause earns its place. It is slightly overloaded for one block but there is little true waste.

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?

There is no output schema, so the description correctly describes the return shape (thread plus full public messages and next_page_token) alongside params, auth, and error codes. For a read-only three-param tool, an agent has everything needed to call it correctly.

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 100%, so the schema already documents inbox_id, thread_id and limit. The description repeats those same constraints (thr_ prefix, default 100/max 200) without adding new syntax or format detail beyond the schema. 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?

States a specific verb and resource with clear scope: every message in one conversation, oldest first, including extracted_text. This implicitly separates it from cooper_get_message (single message) and cooper_list_threads (listing threads), though no sibling is named explicitly.

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 opening clause gives a clear trigger condition ('when you need every message in one conversation'), which is genuine when-to-use guidance. It stops short of naming alternatives or stating when-not to use it (e.g., versus search_threads or list_messages).

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