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

Annotations already cover safety (readOnly, openWorld, idempotent), and the description adds genuinely new behavior: the result cap, the exact returned fields, the privacy guarantee that publisher/maintainer emails are never returned, and the paid x402/USDC flow including what happens on an unpaid call. This is exactly the value-add the annotations cannot provide.

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, purpose front-loaded, then return shape, then payment mechanics — no filler. The second sentence is long and packs privacy plus pricing into one block, but every clause carries information.

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?

With no output schema, the description correctly compensates by listing returned fields, and it covers the non-obvious paid-invocation path. Remaining gaps are minor: no pagination/offset guidance beyond the cap and no error behavior beyond the payment case.

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% ('Search text.' and 'Max results (1-20).'), so the schema carries the parameter burden; baseline is 3. The description lightly enriches q by saying it accepts a keyword or name and restates the 20-result cap, but adds no syntax, matching, or ranking detail beyond 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?

States a specific verb+resource ('discover npm packages by keyword or name') and enumerates the returned fields, so the agent knows exactly what this tool produces. It is clearly a keyword/name search rather than a single-record lookup, which implicitly separates it from npm_package/npm_version, but no sibling is named 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?

'Use to discover npm packages by keyword or name' gives clear context for when to reach for it, and the payment note ('call without payment to receive the PaymentRequired object') gives actionable invocation guidance. However, it never states when NOT to use it or which sibling to prefer for exact-name/version lookups.

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