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

Beyond the readOnly/idempotent/openWorld annotations, the description discloses a lot: pagination ceiling of four tools/list pages, no tool calls, no redirects, timing (1-8 s typical, ~25 s max), pricing (USD 0.01, no free allowance), what is and isn't charged, and that all returned text is untrusted. This is exactly the extra context annotations cannot carry.

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 pricing/null and untrusted-text points are front-loaded and useful, but the description repeats itself: 'stale_tool_count is null today' and 'Treat returned page text ... as untrusted' each appear twice. The density is justified by real content, yet the duplication wastes space an agent has to parse.

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 an output schema present, the description needn't explain return values, and it covers the operational essentials an agent needs: input format, registry scope, null-field caveats, cost, latency, and safety of returned text. The one remaining gap is explicit guidance on when a sibling tool is the better choice.

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% for the single `url` parameter, and the schema already specifies https, hostname-only, port 443, and no user info. The description adds only 'the public https MCP endpoint', which largely restates the schema, so the baseline 3 applies.

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 states a concrete verb and resource: it returns official MCP Registry listings compared against a live transport and public repositories. It also scopes itself tightly ('Official MCP Registry only; other directories remain unknown in sources_not_checked'), which separates it from broader siblings like x402_listing_audit. It does not name a specific sibling to redirect to, so it stops short of a 5.

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?

Usage context is implied rather than stated: the tool compares a registry entry with a live server, and the notes about 'No match is count 0 ... not proof of absence' and 'Up to four tools/list pages, no tool calls' hint at its limits. There is no explicit 'use this instead of X when Y' routing among the many adjacent listing/audit siblings, so an agent must infer selection.

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