Close a Runtime Session

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

Annotations already indicate readOnlyHint=false and destructiveHint=false, so the mutation is not purely read-only and not destructive. The description adds meaningful context by mentioning 'tamper-evident evidence history', which tells the agent the operation preserves audit integrity and is not a full deletion. This goes beyond the annotations and helps clarify expected behavior.

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?

The description is one concise, complete sentence that front-loads the primary action and adds a valuable qualifier. It contains no redundant phrases and is appropriately sized for a tool with two parameters.

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?

Given the 100% schema coverage, an output schema, and the supportive annotations, the description provides sufficient context for an agent to invoke the tool correctly. It does not spell out the exact response format, but the output schema is present, so that is not required. It could have added a note about idempotency, but idempotentHint=false already communicates that.

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 the schema already documents both parameters: session_id and reason. The description adds no new parameter-level detail beyond what the schema provides, and the tool description stays at a high level. A baseline of 3 is appropriate because the schema carries the parameter documentation burden.

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?

The description states a specific verb ('Mark... closed') and resource ('session') with a distinctive qualifier ('preserving its tamper-evident evidence history'). This clearly differentiates session_close from sibling operations like session_status, session_start, and checkpoint_save, so an agent can understand it without needing further context.

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?

The description implies the tool is used when a session should be closed while keeping its evidence history intact, but it does not explicitly state when to use it versus alternatives such as checkpoint_save or record_outcome. There is a clear contextual signal, yet no explicit when/when-not guidance.

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