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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false; the description adds that the session's held resources are freed (the actual side effect) and restates that re-closing is harmless, reinforcing the idempotent behavior in agent-facing language. It stops short of describing what a close does to in-flight work, but the core effect is disclosed.

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 zero waste: the effect comes first, the required input second, the edge case last. Every clause carries information an agent needs.

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-parameter teardown tool with full schema coverage, an output schema, and rich annotations, the description covers effect, input, and idempotency. Only failure handling for an unknown sessionId is unaddressed, a minor gap given the annotations already mark it non-destructive and idempotent.

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% and the single `sessionId` parameter is already documented in the schema as the value session_call returned. The description's 'Pass the `sessionId`' adds no syntax or format detail beyond the schema, so 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 ('Ends a session') and ties it directly to the sibling that created it ('a session `session_call` opened'), so an agent knows this is the counterpart to session_call and not one of the many jig_* lifecycle tools.

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?

Implies the correct sequencing (call after session_call) and explicitly says pass the `sessionId`, which is the only required input. It does not name an alternative for releasing resources (e.g. llm_detach) but no competing close tool exists among the siblings, so the guidance is nearly complete.

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