Verify whether a package name exists in a specified ecosystem registry before using it in install commands or validating generated names. Returns boolean.
Boolean registry existence check. USE WHEN: about to emit a package name in an install command but unsure it exists; verifying a name generated from training data. RETURNS: {exists}.
| Name | Required | Description | Default |
|---|---|---|---|
| ecosystem | Yes | ||
| package | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations (readOnly, idempotent), the description reveals the return format ({exists}) and positions the tool as a registry check, implying remote lookup. It doesn't discuss rate limits or failure modes, but the annotations already cover the safety profile, so the added context is useful.
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 extremely concise: one main clause plus 'USE WHEN' and 'RETURNS' sections. No wasted words; each segment adds value and the structure is front-loaded with the core purpose.
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?
For a simple boolean check with read-only annotations, the description covers purpose, usage, and return shape. However, it omits parameter explanations and error/edge-case behavior, leaving minor gaps for a simple tool. The absence of an output schema is mitigated by the explicit return format.
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 description makes no mention of the 'package' or 'ecosystem' parameters. With schema_description_coverage at 0%, the description provides zero parameter semantics, forcing the agent to rely solely on the schema's type/enum definitions. There's no compensation for the low coverage.
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 'Boolean registry existence check,' a specific verb-noun phrase that clearly identifies the tool's function. It distinguishes from sibling tools like check_malicious or check_typosquat by focusing solely on existence, and the 'RETURNS: {exists}' adds further clarity.
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 provides explicit 'USE WHEN' conditions, including checking before emitting an install command and verifying training-data-generated names. It lacks when-not scenarios or alternative tool references, so it's clear but not fully differentiated from siblings.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.