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

Annotations already declare destructiveHint=true, readOnlyHint=false, and idempotentHint=true, so the safety profile is covered. The description adds a genuinely non-obvious behavioral consequence beyond the annotations: the session handle becomes invalid after the call, which tells the agent this operation cannot be retried with the same handle.

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 short sentences, with the action and its optional modifier front-loaded and the side effect placed second. 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?

An output schema exists, so return values need no explanation, and the one critical side effect (invalidated session) is disclosed. Coverage is strong for a small tool, with only minor omissions such as error behavior when the session is already gone.

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 both 'session' and 'say' are already documented in the schema (including the 4000-char limit). The description's mention of an optional goodbye adds a usage example but no semantics beyond the schema, 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?

States a specific verb and resource ('Leave the call') and clarifies the optional narration behavior, so an agent can distinguish it from siblings like join, say, and next. It does not explicitly name an alternative tool the way a 5 would, but the purpose is unambiguous.

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 rather than stated: the parenthetical about optionally speaking 'say' first signals it is the terminal action in a call lifecycle, and 'session handle is invalid afterwards' hints at when it cannot be reused. There is no explicit when-to-use/when-not guidance or named alternative.

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