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

Annotations already declare readOnly/idempotent/non-destructive, so the description rightly focuses on things annotations cannot convey: the 5-credit cost and a concrete disclosure that possession coverage is missing for specific league-season combinations and that its average is computed only over matches that have it. That coverage caveat materially affects interpretation of returned numbers.

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, then caveats, then cost — every sentence carries information. The metric enumeration is long but functional, since it defines the scope of the response.

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?

An output schema exists, so return values need not be described; with that off the plate, the description covers scope, a known data-quality limitation, and cost. Only the absence of alternative-tool routing keeps it short of 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?

Schema coverage is 100%, so team, league and season are fully documented in the schema, establishing the baseline of 3. The description only indirectly touches parameters by naming leagues (Eredivisie, Scottish Premiership, NWSL) in the coverage caveat, adding no format or 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?

States a specific verb-and-resource: per-match season averages for clubs, split into for and against, with an explicit metric list. That makes it distinct from get_standings, get_ratings and get_leaders, though those siblings are never named as alternatives.

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?

'Use for clubs' per-match averages over a season' gives an implied usage context, but there is no when-not guidance and no pointer to the sibling tools an agent should pick for standings, ratings or team-level season totals.

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