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

The description goes far beyond the annotations (readOnlyHint, openWorldHint, idempotentHint). It discloses that the tool fans out across multiple external services, explains partial failure behavior, explicitly mentions a 5-30s timeout for first measurements, and introduces the 'sources_failed' field. This is rich behavioral context that annotations cannot convey.

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 a dense but well-structured paragraph. It opens with the core purpose and then systematically adds details (data sources, use case, return fields, ecosystem limitation, failure handling) without redundancy. Every sentence earns its place; no filler.

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, so the description carries the full burden of explaining return values. It enumerates the exact summary fields, per-advisory details, links, and alternative versions. It also covers the main edge case (bundlephobia timeout) and the ecosystem restriction. For a composite tool with no output schema, this is complete.

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 fully documents both parameters (package, version) with clear descriptions, including scoped package support and default version behavior. The description adds no new parameter-level semantics beyond implying npm-specific context, 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 opens with a clear verb+resource: 'Composite should I add this npm package to my project check in ONE call' and specifies the underlying data sources (deps.dev, bundlephobia). It clearly distinguishes this tool from siblings by naming the exact ecosystem (npm) and the data providers, so an agent knows precisely what it does.

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 states when to use it: 'Use whenever an agent asks "is X safe / popular / small" or "what does adding lodash cost me"'. It also gives exclusion criteria: 'NPM ecosystem only in v1' and directs other ecosystems to a different tool (deps.dev:version directly). This is exemplary when-to-use guidance with alternatives.

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