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

Annotations already indicate this is not read-only (readOnlyHint=false), and the description adds the prerequisite of a pending invite. It does not disclose consequences such as leaving a current faction or potential failure reasons, but for a simple join action this is acceptable.

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 sentence with a parenthetical note, immediately stating the action and the key prerequisite. No wasted words.

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 two-parameter join action, the description covers the essential action and precondition. However, given the presence of similar siblings like 'faction_accept_invite', a note clarifying this is the player accepting an invitation would improve completeness.

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 already provides descriptions for both parameters (session_id and faction_id) with 100% coverage, including the pending invite requirement for faction_id. The description adds no additional parameter semantics beyond 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 'Join a faction via invitation' with a clear verb and resource, and notes the prerequisite of a pending invite. However, it does not distinguish from sibling tools like 'faction_accept_invite', which may represent a similar action, so it lacks sibling differentiation.

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 should only be used when the player has a pending invite from the faction, which is a clear precondition. It does not explicitly mention alternatives (e.g., 'faction_decline_invite' to decline or 'create_faction' to start your own), so guidance on when not to use it is missing.

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