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

Beyond the annotations (readOnly, openWorld, idempotent), the description adds substantial behavioral context: the answer is deterministic, sourced from the real published artifact, signed, and includes typosquat-adjacency flags on misses. It also discloses rate limits and shared quota with /demo/v1/* HTTP routes, which is valuable for the agent.

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 three sentences long with every sentence adding value: purpose, behavioral details, and rate limits. It front-loads the core question and avoids any fluff or repetition of schema fields.

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?

Given the simple parameter set and the existence of an output schema, the description covers purpose, behavior, constraints, and alternative access routes. It is complete for this tool; no critical information is missing.

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 0% schema description coverage, the description compensates by explicitly mentioning both parameters: 'PyPI or npm' clarifies the ecosystem enum, and 'package name' explains the name parameter. This gives the agent enough semantic understanding even though the schema omits descriptions.

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 direct question that precisely defines the tool's capability: determining whether a PyPI or npm package name exists. This is a specific verb+resource (exists + package), clearly distinguishing it from sibling tools like symbol_exists and version_diff.

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 gives clear context for when to use this tool (package existence checks) and provides usage policy details including free quota limits and a paid HTTP route for higher volume. It does not explicitly name alternatives but the purpose is unambiguous, so no exclusions are needed.

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