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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so safety is covered; the description adds genuine non-annotation behavior — determinism, balanced home/away, byes for odd team counts, and the exact double round-robin transformation (reversed round order plus home/away swap on the return leg). It stops short of error/prerequisite behavior (e.g. uniqueness of team names, invalid weekday handling).

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 dense sentences with the core purpose front-loaded, then the algorithm variant, then the outputs. No filler and nothing repeated needlessly.

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 enumerated, and annotations carry the safety profile; the description nonetheless names the returned artifacts (fixtures, counts, Markdown table, share link), which is mildly redundant but harmless. Remaining gap is minor: no note on failure modes or input validation behavior.

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 50% (weekday and startDate are documented in-schema; teams and doubleRoundRobin are not), and the description only partially compensates by explaining the double round-robin effect and the 3–24 team bound. It adds no meaning for the teams array itself beyond the schema's maxLength/minItems constraints.

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 (Create) and resource (deterministic weekly fixtures) with hard scope: 3–24 teams, balanced home/away, odd-team byes. The round-robin domain is clearly distinct from the siblings (formation, lineup, playing-time), so an agent can select this without ambiguity.

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?

Usage is implied by the stated scope and constraints, but there is no explicit when-to-use/when-not-to-use guidance and no routing to or away from siblings. It never says, for example, whether this is the right tool when you already have a fixture list or how it relates to generate_fair_lineup.

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