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

Annotations already establish the safe read-only/open-world profile, so the description's job is to add context — and it does, enumerating exactly what comes back (opponent, kickoff, OUT and QB-gate flags, best price per side) plus the Pro-tier projection gate. It does not mention rate limits or data freshness, but the added payload detail 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?

Three sentences, trigger phrasings front-loaded, then inputs, then returned content. Slightly dense in the enumeration clause, but every clause describes real returned data rather than 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?

There is no output schema, so the description has to characterize the return shape — and it does so item by item, including the market-pricing and Pro-tier caveats. What remains thin is how multiple leagues are disambiguated and whether the username is strictly required, though the schema partially covers the latter.

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% and both parameters are already documented in the schema, including the 'when the user is in several' condition for league. The description restates that same condition for league and adds only that the username is required in practice, so it adds little beyond the structured fields. Baseline 3 applies.

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?

The description opens with literal user triggers ('show my fantasy team', 'what is Kalshi pricing my starters at') and then states the concrete resource: roster, starter matchups, and per-starter Kalshi strikes. This is distinguishable from siblings like player_outlook or start_sit, which do not mix roster display with market pricing.

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?

It clearly states when to reach for this tool via quoted user phrasings, and implies the input condition for the league parameter. It never names a competing sibling or an exclusion, so it stops short of a full routing statement.

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