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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is fully covered. The description adds only the framing that the result is a summary (metadata-level) rather than message content. It says nothing beyond annotations about ETag/304 conditional behavior or multi-mailbox scoping, both of which live only in the schema.

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?

Two sentences, zero filler, with the positive usage stated first and the routing alternative second. Nothing repeats the name or title and nothing is buried.

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?

An output schema exists and the input schema fully documents all three parameters, so the description need not explain return values or parameter formats. For a simple read tool this is close to complete; only the conditional-request behavior is left to the schema rather than reinforced.

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% and includes the nuanced mailbox_id targeting rule and If-None-Match semantics, so the schema carries parameter meaning. The description restates thread_id but adds no syntax, format, or precedence guidance beyond it. 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 ('read one thread summary by thread_id') and explicitly frames the return as a summary rather than full messages, which is the key distinction from mailbox_list_thread_messages and qubrics_mailbox_list_threads. An agent can pick it out of a very large sibling set without opening the schema.

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?

Names the alternative tool explicitly ('mailbox_list_thread_messages') and gives the condition that selects it ('when the task needs the messages in the thread'). This is the primary confusion risk for a thread-summary tool, and it is resolved directly.

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