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

Annotations already declare a safe read-only, closed-world operation, so the bar is lower. The description then adds genuinely useful behavior: the shape of returned rounds ({home, away}, resting or null), the game count, an auxiliary group-chat message, and the refusal-with-reason path. It stops short of describing pagination or ordering of rounds, but the added context is substantial.

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 core scope is front-loaded in the first clause and every subsequent clause carries real information (resting team, return shape, dedup, refusal). It is packed into one long sentence, which slightly hurts scanability, but there is no filler.

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 only two simple parameters and no output schema, the description carries the return-shape burden itself and covers limits, dedup, byes, and error behavior. An agent has everything needed to call and interpret this tool correctly.

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 the baseline is 3. The description still adds meaning beyond the schema: it clarifies the dedup rule for 'teams' ('repeated names count once'), the valid 3–16 range, and the consequence of odd counts (a resting team each round), which sharpens how 'homeAndAway' interacts with the round structure.

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 ('Make a round-robin fixture list') with its exact scope (3 to 16 teams, everyone plays everyone). It is clearly distinguishable from siblings like make_fair_teams and reshuffle_teams without opening any schema.

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 supplies strong input constraints (3–16 teams, duplicates collapse, out-of-range names are refused) which implicitly tells the agent when the tool is usable. However, it never contrasts this tool with any sibling such as make_fair_teams or pick_teams, so selection guidance remains inferential.

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