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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds a genuinely non-obvious privacy note ('Muffed stores nothing about the requester'), but says nothing about rate limits, error behavior when a username doesn't exist, or result size.

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 short sentences, front-loaded with the core action and zero filler. Efficient, though the trailing sentence about what Muffed stores is slightly tangential to the tool's invocation.

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?

For a simple read-only lookup this is close to adequate, and annotations cover the safety profile. However, with 0% schema coverage the unexplained 'season' parameter and the absence of any output shape detail leave gaps an agent must guess at.

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 0% for two parameters. The description only implies the username input and completely ignores the optional 'season' parameter (YYYY pattern), so it does not compensate for the documentation gap in the schema.

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 specific verb and resource ('Lists the NFL leagues a Sleeper username belongs to') and specifies the payload ('with each league's id'). It is distinguishable from the sibling sleeper_get_league, which implies fetching one league's detail, though it never names that sibling explicitly.

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?

There is no guidance on when to use this tool versus sleeper_get_league, sleeper_standings_story, or the other sleeper siblings. No prerequisites or exclusions are given, so the agent must infer usage purely from the one-line purpose.

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