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

Annotations already mark the tool read-only and idempotent; the description adds non-obvious behavior: the response defaults to a compact summary shape, is ordered by most-recently-updated, and can be expanded via detail='full' to include battlemap refs and full descriptions. It does not mention the sort='date' option, but the schema covers it.

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?

Three compact sentences, front-loaded with the core purpose, then defaults, then configuration options. Every sentence adds information and there is no filler.

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 read-only list tool with an output schema, 100% schema coverage, and clear annotations, this description provides all selection and invocation context: scope, default ordering, response shape, and how to request full detail or cap results. Nothing material is missing.

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 100%, with every parameter (sort, limit, detail) already described in the input schema. The description reinforces detail and limit but adds no new parameter semantics beyond the schema, so the 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?

The description opens with a clear verb and resource: 'List sessions the calling user is part of across all their campaigns (DM or player).' This scope distinguishes it from sibling tools like play_list_campaign_sessions (campaign-scoped) and play_get_session (single session).

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?

It clearly states this is the cross-campaign, user-centric listing tool ('across all their campaigns'), which implies when to prefer it over campaign-scoped alternatives. However, it does not explicitly name a sibling or state when not to use it, so it stops short of a 5.

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