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

With readOnlyHint/openWorldHint already declared, the description still adds real context: this is live market data, best price per side is computed, and weekly projections are gated behind Pro. It does not say whether prices are delayed, whether a missing/unknown username errors out, or how much data a response can carry.

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?

Two sentences, both earning their place, with the usage triggers front-loaded. The second sentence is a fairly dense comma-list of return fields, but each item is informative 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 must describe return values and it does so thoroughly, including the tier-gated projection. Missing only edge behavior: no-username defaults, empty leagues, and whether an unresolvable league name fails or falls back.

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% and both parameters are already documented, so the schema does the heavy lifting. The description only restates the username/league relationship; notably all parameters are optional and it never says what happens when sleeper_username is omitted, which is the one ambiguity the schema does not resolve.

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 states a concrete verb+resource pair ("show my fantasy team", Kalshi pricing for starters) and enumerates exactly what comes back: roster, opponent, kickoff, OUT/QB-gate flags, and prop strikes with best price. It implicitly separates itself from advice tools like start_sit by labeling the output "market data" rather than recommendations, though no sibling is named outright.

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 gives explicit trigger phrases ("show my fantasy team", "what is Kalshi pricing my starters at") plus the input condition for the optional league argument ("if you have several"). There are no explicit when-not conditions or named alternatives such as start_sit or player_outlook, so it stops short of a 5.

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