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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true, so the description does not need to restate those. The description adds a useful behavioral detail: the caller must be a member of the session's campaign, which is a permission requirement not covered by annotations. However, it does not disclose other behavioral aspects like return format or potential errors, but annotations cover the safety profile.

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 two concise sentences, with the key action and object front-loaded. The second sentence adds a necessary permission note. No extraneous words or redundant information.

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 tool's simplicity (single parameter) and the presence of a rich output schema (as indicated by has_output_schema=true), the description is sufficient for an agent to call it correctly. The permission requirement is a key contextual element. The only minor gap is not specifying that the output schema provides the return structure, but that is expected.

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?

The schema covers 100% of parameters with a description for 'id', so the description does not need to add much. The description implies the ID refers to a session and that it is the primary key, which is consistent with the schema. No extra nuance is provided that isn't already in the schema.

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 ('Fetch'), resource ('one session by id'), and scope ('including its notes, battlemap references, and session-image attachments'). It is clear and distinct from siblings like play_get_page or play_list_campaign_sessions, which serve different purposes.

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 clearly states the primary use case (fetching a session by ID) and implies it should be used when a specific session is needed, rather than listing sessions (play_list_campaign_sessions). However, it does not explicitly state when not to use it or name alternatives, but the context is clear enough.

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