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

While annotations already mark the tool as read-only, open-world, idempotent, and non-destructive, the description adds substantial behavioral context: composite fan-out across two services, return shape (summary block fields, per-advisory detail, links, alternative versions), and degradation behavior. It discloses that bundlephobia's first measurement can take 5-30s and that sources_failed will list failures. This goes far beyond annotations and helps manage agent expectations.

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, covering purpose, usage, return fields, ecosystem limitations, and timeout behavior in a single paragraph. The core purpose is front-loaded and every sentence earns its place. It is longer than the simplest examples but justified by the tool's composite nature.

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?

There is no output schema, but the description compensates thoroughly by enumerating the summary block fields, per-advisory detail, links, and alternative versions. It also addresses failure modes (partial failures, sources_failed list) and ecosystem constraints. For a composite tool with no output schema, this provides a complete picture for an agent.

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% with both `package` and `version` already described in JSON Schema. The description does not add new meaning about parameters; it mentions "specific version" and "latest" but these are already in the schema. Baseline 3 is appropriate since the schema fully carries parameter documentation.

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 opens with a specific verb+resource: 'Composite "should I add this npm package to my project" check in ONE call', clearly stating it scans npm packages. It distinguishes from siblings by naming the fan-out across deps.dev and bundlephobia and the exact question it answers (safety, popularity, size). This is unambiguous and unique.

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?

Explicit usage guidance is provided: 'Use whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me"'. It also gives an exclusion and alternative: 'NPM ecosystem only in v1; PyPI / Maven / Cargo / Go fall under deps.dev:version directly'. This tells the agent both when to use this tool and when to use an alternative.

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