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

Annotations already declare readOnly, idempotent, closed-world, non-destructive, so safety is covered. With no output schema, the description contributes real behavioral value by disclosing exactly what the card contains (injuries, price-change progress, ownership, penalty share), though it says nothing about caching, rate limits, or failure when a name is ambiguous.

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?

A single dense sentence that front-loads the imperative "Use this for" and the player-count constraint before listing outputs. Efficient, though the output enumeration makes it long and it could have been split for scannability.

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?

Given no output schema, the description usefully enumerates the returned fields, and the player-count limit and default horizon are handled between description and schema. Horizon semantics (gameweeks counted, 1-8) are only in the schema, and there is no note on empty/unknown-player results, so it is strong but not fully 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 description coverage is 100%, so both names and horizon are fully documented in the schema; the description only reinforces the 1-5 player bound already enforced by minItems/maxItems and says nothing about the horizon parameter or name-format expectations. Baseline 3 when the schema does the heavy lifting.

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 resource (FPL player cards) and an exact scope (one to five players), with a concrete enumeration of what comes back (expected points, fixtures, injury news, price, ownership, xG/xA, penalty share). It only implicitly separates itself from siblings like get_player_breakdown and find_players, so it falls short of a 5.

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 this for one to five FPL players" gives a usage condition (card lookup for a small set of named players), but it never names alternatives such as find_players for discovery, compare_players for side-by-side, or get_player_breakdown for deeper stats, leaving the agent to infer when this tool wins.

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