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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds what is actually returned (capabilities, sports, credentials) and the prerequisite state (no connected profile), which the annotations cannot convey; the trailing note about league tools being read-only and share publishing on request is background about siblings rather than this tool.

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?

Purpose and the expected return contents are front-loaded in the first clause, and the 'start here' routing cue follows immediately. The final sentence about other league tools is off-topic for this tool and dilutes focus.

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?

No output schema exists, so the description must hint at return content, and it does list capabilities, sports and required credentials. The response_format option is left to the schema, which is acceptable at full coverage, but an agent gets no sense of the response shape.

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 single response_format parameter has 100% schema description coverage, including enum meaning and default, so the schema carries the semantics. The description says nothing about output format options, so no credit above the baseline.

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?

Names the specific resource (supported platforms) and enumerates them (fantrax, espn, sleeper) with the returned attributes (capabilities, sports, required credentials). The parenthetical user question plus the 'start here when NO profile is connected' clause makes it clearly distinguishable from fantasy_get_my_setup and fantasy_list_user_leagues.

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?

Gives an explicit trigger: use it when no profile is connected, since a connected profile's leagues are already configured. No sibling is named as an alternative, and the when-not case is only implied via the connected-profile caveat, so it falls short of a full 5.

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