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

Annotations already cover read-only, idempotent, and non-destructive, so the bar is lower. The description adds real value beyond them: the error behavior for unknown slugs and the free-tier cost (100 calls/day without a key).

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?

Compact and front-loaded: what it returns first, then example, then error case, then cost. Every clause carries information, though the inline JSON example is slightly noisy.

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 needn't be explained, yet the description gives a useful summary anyway. Error behavior and rate limits round out what an agent needs for this simple read tool.

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 the single slug parameter is already documented with the same example values the description repeats, so little is added. The example mapping {"slug":"trustmrr"} reinforces the semantics but is largely duplicative.

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 and resource ("Returns one tag") and enumerates the payload fields (count, median annualized revenue, members with rank and revenue), so the agent knows exactly what it gets. Sibling differentiation is absent: nothing distinguishes it from get_category or list_tags.

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?

Provides a concrete lookup example and the failure condition (unknown slug -> isError), which implies when to use it. It never states when to prefer list_tags or get_category, so routing between siblings is left to inference.

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