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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered structurally. The description adds genuine behavioral context beyond that: the three output formats including a token-minimizing 'slim', and the important fallback that a registry server absent from the directory still returns its registry entry. It doesn't mention rate limits or error behavior, which keeps it below 5.

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 core action and identifier source are front-loaded in the opening clause, and nearly every phrase carries new information. It loses a point for being a single long comma-spliced sentence that takes effort to parse rather than being broken into distinct statements.

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 appropriately carries the burden of describing the return payload field by field, which it does. Coverage of format trade-offs and slug resolution is sufficient for correct invocation; only minor gaps like pagination or error shape remain, and those are not essential here.

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%, so the baseline is 3. The description still earns credit above baseline by explaining that the slug accepts alternative identifiers (package name, GitHub owner/repo, registry name) and that the response reports which slug the input resolved to — resolution semantics the schema description only partially conveys.

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?

States a specific verb and resource ('One listing in full by its slug') and immediately ties the slug source to the sibling search_tools, so an agent can distinguish retrieval from discovery without opening a schema. The enumerated payload (snippets, auth, prices, provenance, hosted tools, changes) makes the scope concrete.

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 parenthetical '(from search_tools)' establishes the expected workflow: search first, then fetch by slug. The format note gives a hint about when to prefer slim over json, but there is no explicit statement of when not to use this tool or which siblings (e.g. check_server, verify_listing) cover overlapping ground.

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