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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is covered. The description adds genuinely new behavioral context: the session handle becomes invalid afterwards, warning the agent not to reuse it. Missing only edge-case detail such as behavior on an already-invalid session.

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 tight sentences, zero filler, with the core action and the session-invalidation consequence both front-loaded. Every clause earns its place.

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 two-parameter mutation tool with an output schema and full annotation coverage, the description supplies the essential post-condition (invalid session). Only minor gaps remain, e.g. what happens if the session is already gone, which the idempotentHint partly signals.

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% (both `say` and `session` are documented, including the 4000-char limit and the join provenance). The description restates the optional `say` semantics but adds no syntax or format detail 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+resource ('Leave the call') that any agent can distinguish from siblings like join, say, or status. The parenthetical clarifies the optional pre-leave utterance, which sharpens rather than muddies the purpose.

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?

Makes clear this is the tool for exiting a call and notes the optional pattern of speaking a goodbye first. It does not explicitly contrast with alternatives (e.g., why not just stop calling `next`), but the usage context is unambiguous and no exclusions are needed.

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