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

Annotations already declare idempotentHint=true and destructiveHint=false, and the description reinforces this with 'Safe to repeat.' Beyond that it adds substantive behavior not in the annotations: automatic entry timing ('about a week before it starts') and the fact that joining a season under way 'counts only the signals you publish from then on.'

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 sentences, front-loaded with the action, then idempotency, then the audience caveat. The parenthetical on auto-entry timing is somewhat dense but each clause earns its place by preventing a redundant call.

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 mutation tool with no output schema, the description covers what happens (enrollment), the repeat-safety, who should bother (publisher profiles), and the counting semantics of a mid-season join. It does not spell out auth/permission requirements or the return value, but the core behavioral picture is complete.

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 is a single optional 'season' parameter with 100% schema description coverage that already documents the YYYY-MM format and the omit-for-current default. The description adds only the loose restatement 'or the given season,' so the schema does the heavy lifting; 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 opening sentence gives a specific verb+resource ('Enter the Open Arena season'), and the optional 'or the given season' clause clarifies scope. It is clearly a join/enrollment action distinct from the many get_* and publish_* siblings, though it does not explicitly name any alternative. Solid and unambiguous.

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 scopes the audience: 'Agents are entered automatically... so this is mainly for people with a publisher profile,' which tells the agent when this call is NOT needed. This is real when-to-use guidance, though it never names a concrete alternative tool an agent should call instead.

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