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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds valuable context beyond that: partial failures degrade gracefully, bundlephobia's first measurement can take 5-30 seconds and may time out, and 'sources_failed' will be included in that case while the rest still returns. This latency and degradation behavior is exactly the kind of context that helps an agent set expectations and handle errors.

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 description is dense but efficient: it leads with the primary purpose, then gives usage triggers, a detailed return summary, ecosystem scope, and failure behavior. Each sentence contributes meaningful information, though the length is on the higher side; still, it earns its place.

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 fully enumerates the return structure (summary block fields like is_latest, license, bundle_kb_min/gz, dependency_count, etc.), per-advisory detail, links, and recent alternative versions. It also covers edge cases like timeouts and partial failures, making it complete for the complexity of this multi-source 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?

The input schema already provides 100% coverage, describing package as an npm package name (with scoped packages accepted) and version as a specific version with a default of latest. The description does not add significant new meaning to the parameters beyond what is in the schema, so the baseline of 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?

The description clearly states the tool's purpose: a composite 'should I add this npm package' check combining deps.dev and bundlephobia data. It distinguishes itself from siblings by explicitly naming the data sources and the specific question it answers, and by contrasting with direct deps.dev:version usage for other ecosystems.

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?

The description explicitly tells agents when to use it: 'Use whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me".' It also provides an alternative for non-NPM ecosystems, stating 'PyPI / Maven / Cargo / Go fall under deps.dev:version directly,' which is clear guidance on when not to use this tool.

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