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

Beyond the readOnlyHint annotation, it discloses result ordering (recently active threads vs. oldest-first messages), the fields returned (subject, participants, preview, text, sanitized HTML), and a prompt-injection warning about untrusted message content. That is substantive behavioral context an agent cannot get from the annotations alone.

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 dense sentences, all front-loaded: capability first, mode behavior second, safety warning last. No filler and every clause carries information.

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 3-parameter read tool with an output schema and readOnlyHint, the definition covers both modes, result shape, ordering, and the untrusted-content caveat. Nothing an agent needs to call it correctly is missing.

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 67%, so the schema already documents threadId ('Omit to list threads') and cursor; the description mostly restates the threadId branch while adding the useful detail of what each branch returns and in what order. Baseline 3 is appropriate since the schema carries the parameter burden.

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 an inbox') and crisply splits the two operating modes by return content (thread list vs. thread messages). It does not, however, differentiate itself from the sibling search_inbox, so the agent must infer which read tool applies.

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 clear conditional usage tied to threadId ('Without threadId... With threadId...'), which tells the agent exactly which mode it will get. It stops short of naming when to prefer search_inbox or other read siblings, so there are no exclusions or alternatives.

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