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

Annotations already indicate read-only, idempotent, and non-destructive. The description adds context about the scope ('calling user's accepted friends') and the return content (display name and id), which is useful beyond the annotations. No contradictions.

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 very brief, front-loads the purpose and scope, and adds a single sentence on typical use cases. Every sentence earns its place, with no fluff.

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?

The tool is simple with no parameters, and the description mentions the return fields (name and id), which is sufficient for an agent to know what to expect. An output schema exists, so detailed return structure is likely covered there. Slightly missing is whether the list is sorted or if pagination applies, but for a simple list tool this is adequate.

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?

There are zero parameters, and the schema is empty with 100% coverage. The description clarifies the output fields, which helps agents understand what they'll receive, but parameters are nonexistent, so the baseline of 4 (for no params) is appropriate.

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 clearly states the tool lists the calling user's accepted friends, specifies the returned data (display name and id), and mentions intended use cases (campaign-invite or friend-lookup). It is distinct from sibling tools like play_list_pending_friends and play_find_friend.

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 retrieving accepted friends, distinct from pending friend requests (play_list_pending_friends) and searching for specific friends (play_find_friend). However, it doesn't explicitly state when not to use this tool or mention alternatives, but the use-case mention provides decent guidance.

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