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

Annotations only declare readOnlyHint/openWorldHint; the description adds material cost behavior the agent cannot otherwise know: $0.002 USDC per successful call, x402 payment across Base/Solana/Arc, and no charge on failure. That is exactly the kind of billing and side-effect context an agent needs before invoking a paid 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?

Two sentences, front-loaded with what the tool returns and what it does, then the pricing constraint. No filler or repetition of the title.

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 need no prose, and the single input is fully documented. Combined with read-only annotations plus disclosed pricing and failure-charge policy, an agent has everything required to decide and call correctly.

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?

With one parameter at 100% schema coverage, the schema already documents the exact-name format, scoped packages and the 214-character limit. The description's 'by exact name' merely reinforces what the schema states, adding no format or edge-case detail beyond it.

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 (read-only lookup of one npm package by exact name) and enumerates the returned fields (latest version, license, description, homepage, repository, tarball URL). It also draws a boundary with 'no download counts', so an agent knows exactly what class of data this returns.

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?

'Read-only lookup of one package by exact name' gives clear context for when to use it and constrains the lookup mode, and 'no download counts' excludes a common expectation. It stops short of naming an alternative tool for fuzzy/name-search or download-stat needs, so it is strong but not fully exclusionary.

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