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

Annotations already declare readOnly, openWorld and non-idempotent. The description adds real behavioral context beyond them: grounded only in current docs, includes a code example where available, states the applicable version, cites sources, and crucially 'Says so when the docs don't cover it.' Pricing and paywall behavior are also disclosed. It does not contradict the annotations.

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?

The core answer behavior is front-loaded, but the text is padded: '$0.02' appears in the title and is repeated twice more in the body, and '★ One of our best tools' is marketing that earns no place. The pricing/paywall message is spread across two sentences that could be one.

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 described, and the description covers grounding, sourcing, versioning and the not-covered case. Behavior is well covered for a read-only answer tool; the only soft gap is the exact boundary versus the free docs-lib sibling.

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%, so all three parameters (library, question, ecosystem) are already documented in the schema with examples and an enum. The description only restates the ecosystem families ('npm, PyPI, crates or Go'), adding no syntax or format detail beyond the schema. Baseline 3 is appropriate.

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: 'Ask a coding question about any npm, PyPI, crates or Go library and get an answer written only from its current docs.' It also names the sibling it relates to ('Try docs-lib free first'), letting an agent distinguish this paid tool from the free alternative without opening a schema.

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 clear context ('Ask a coding question about any ... library') and routes to an alternative ('Try docs-lib free first') plus a scoping note ('Paid only, not in the free trial'). It stops short of stating explicitly when the paid answer is worth choosing over the free docs-lib, but the routing intent is clear.

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