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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so safety is covered. The description adds what the list contains (names, countries, file layout) and its prerequisite role for other tools, though it does not mention pagination, rate limits, or error behavior — minor for a zero-param read.

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 sentence front-loads what the tool lists, the scope/quantities, and the returned fields, then closes with the actionable prerequisite note. No sentence is wasted and the call-to-action is easy to locate.

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 must say what comes back, and it does ('names, countries and the file layout'). Combined with zero parameters and full annotation coverage, an agent has everything needed to call it 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?

The tool takes zero parameters, so the baseline is 4; there is no parameter syntax the description needs to compensate for. The description correctly focuses on output content and invocation ordering instead of inventing parameter details.

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 ('Lists') and resource ('every football-data.co.uk league code'), and quantifies scope with '22 main European leagues' and '16 extra-league countries'. It also names the sibling tools it feeds into, so an agent can distinguish it from match_odds and team_results 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?

Explicitly prescribes when to call it: 'call before match_odds/team_results to get a valid code', which both establishes the prerequisite ordering and names the alternatives that depend on its output. Nothing about usage is left to inference.

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