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

readOnlyHint=false signals mutation, and the description adds concrete side effects beyond the annotation: facilities become rent-free immediately, unpaid rent is cleared, and it returns own_faction_station during a battle. These are useful behavioral disclosures, though the exact failure modes (e.g., no invite) aren't described.

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?

Front-loaded with the core action in the first clause, then a dense but informative parenthetical. Slightly overloaded for one sentence, but every clause earns its place.

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 2-param mutation with no output schema, the description covers the precondition, side effects, and the special return case, which is ample. It doesn't explain what happens on an invalid state beyond the invite requirement.

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%, so both parameters are already documented. The description reinforces the invite requirement for faction_id but adds no syntax or format detail beyond the schema, so 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?

States a specific verb+resource ("Join a faction via invitation") and names the mechanism (invitation). However, it does not differentiate from the closely related sibling faction_accept_invite, leaving the agent to infer which of the two to use.

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?

Gives a clear precondition — "You must have a pending invite from the faction" — which is actionable usage context. It stops short of naming alternatives or when-not-to-use conditions, so it's clear but not fully routing.

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