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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered; the description adds genuinely behavioral detail not in the annotations — chronological ordering and decoded message bodies. It does not disclose pagination, thread size limits, or truncation behavior, so it stops short of 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 capability, then the alternative, then the prerequisite. No filler, no repetition of the title.

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, the description carries the return-shape burden and does convey ordering, completeness ('every message'), and decoded bodies. Gaps remain around output size, truncation when maxCharsPerMessage binds, and behavior on very long threads, but it is sufficient to call the tool 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 coverage is 67%: mailbox and maxCharsPerMessage are documented in the schema, but threadId has no schema description. The description compensates by naming the exact source of threadId (search_gmail_messages), which is the one undocumented parameter that would otherwise cause trial and error.

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+resource ('Read every message in a conversation') with scope details (oldest first, decoded bodies), and distinguishes itself from the per-message sibling get_gmail_message and the analogous get_outlook_conversation. An agent can pick this over its nearest neighbor without opening a 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?

Explicitly names the alternative to avoid ('Use this instead of repeated get_gmail_message calls') and the condition that selects it ('when you need the whole exchange'). It also tells the agent where the required threadId comes from (search_gmail_messages), closing the loop on invocation.

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