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

Goes well beyond annotations: declares irreversibility, describes the retention-sweep relationship, notes the main thread exemption, and documents the return shape (success, deleted_session_id, deleted_messages) and error form. Annotations already flag destructive, but the description adds the specifics an agent needs before committing an irreversible action.

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?

Front-loads the action and irreversibility warning, then rationale, exclusion, args and returns. Structured with clear sections; slightly verbose with the retention-sweep aside but every part informs the agent's decision.

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 single-param destructive tool with no output schema, the description covers purpose, irreversibility, exclusions, the parameter, and the exact return payload. Nothing material is missing for correct invocation.

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 0%, so the description must compensate; it documents the sole parameter session_id as 'The chat session's ID' and clarifies the return includes deleted_messages count. Minor gap: does not state the type is an integer or how to obtain the ID, but adds enough meaning.

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 (delete) and resource (agent chat session) with clear scope: 'including every message in it.' Distinguishes the target from the sibling get_agent_chat_session and list_agent_chat_sessions, and explicitly notes what cannot be deleted (the persistent main conversation thread).

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?

Explains when to use it (users clearing a session immediately, e.g. shared context no longer wanted) and contrasts with the automatic 90-day retention sweep, plus an exclusion (main thread cannot be deleted). Clear context but no explicit named alternative sibling; strong but not exhaustive of when-not scenarios.

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