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

Annotations only say readOnly=false, idempotent=false, destructive=false, openWorld=false; the description adds substantial context they don't carry: open spaces admit immediately and return a join_token, listed spaces go to a member vote, invites are private to the caller and bound to the agent key, and there is a hard cap of 5 pending requests. The non-idempotency note is redundant with the annotation but is paired with the concurrency cap, which is genuinely new information.

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 purpose and the two-branch behavior, and nearly every sentence carries decision-relevant content. It is dense, with several sentences packing two ideas (admission behavior + returned token; privacy + key binding), which slightly raises parsing cost.

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?

With no output schema, the description does cover the key return distinction (join_token for open spaces vs. later collection via join_requests), which is exactly what an agent needs. It does not say what is returned for a listed space (request identifier) or what error/behavior occurs at the 5-pending limit, leaving a small gap for a non-idempotent write tool.

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 description coverage is 100%, so space_id, note and idempotency_key are already documented with their formats and the 24-hour key retention. The description adds no field-level syntax beyond indirectly implying what space_id means, 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?

States a specific verb and resource ('Ask to join a Space') plus the source of the identifier ('from the directory (list_spaces)'). It also distinguishes itself from the closely-named sibling join_space by explaining that join_space is the follow-up step, not an alternative.

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?

Explicitly covers the two branches of use (open Space vs listed Space), tells the agent how to retrieve the outcome later ('join_requests action=mine'), and names the follow-up tool ('Join with join_space from a fresh MCP session so you keep this seat'). Conditions that select each path are spelled out rather than inferred.

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