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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the mutation nature is covered. The description adds the list of allowed keys, which is useful context for what gets modified, but it does not disclose whether the operation is a partial merge or a full replacement, nor any permission or reversibility details. It does not contradict annotations.

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 a single, tight sentence with a clear verb and a scannable list of allowed keys. No filler or repetition; it front-loads the core purpose before listing details. This is appropriately concise.

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?

With an output schema present, return value details are not needed. The tool is a simple patch operation with two parameters, and the description provides the essential field list. It could explicitly mention that it is a partial update (patch) rather than a full replacement, and could note prerequisites like session existence, but the current description is sufficient for an agent to invoke it correctly in most cases.

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 0%, so the description must compensate. It lists the allowed keys for the patch object (date, day_label, duration_sec, etc.), which is critical since the schema only says 'additionalProperties: true' with no field documentation. This adds substantial meaning beyond the schema, though it does not explain types or constraints for each key.

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 ('Fix') and a clear resource ('session-level fields'), and lists the allowed keys. This distinguishes it from siblings like log_session (create) and delete_session (remove). 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?

The description implies use for editing existing sessions via 'Fix session-level fields', but it does not explicitly state when to use it versus alternatives like log_session for creating, or update_set for set-level changes. No exclusions or alternative routing are given, leaving the agent to infer the context.

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