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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered without the description. The text adds scale context (indexed across 18,204 packages and 16,170 remote servers), which is useful, but omits behavior an agent would want: whether naming a server triggers a live network lookup, any rate limits, and what happens with no argument at all.

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?

Two sentences with no filler, and the output inventory is front-loaded. The first sentence is a dense four-item enumeration that reads slightly run-on, but nothing is wasted.

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 read-only analysis tool with no output schema and 0 required parameters, the description does state the classes of result returned. The notable gap is the all-optional input surface: it never explains the default behavior when neither tools nor server is provided, which is the exact ambiguity an agent is most likely to hit.

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 description coverage is 100% and the two parameters are already documented there ("A tools/list result", "Or a server HISTOR observes: https endpoint, npm:<package>..."). The description's "Send a tools/list or name a server" only restates the schema's field meanings rather than adding format or precedence detail, 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 specifies the analysis performed (token cost an MCP server's tool list adds to every request, cost per 1,000 requests, heaviest tools, rank) which is specific enough for an agent to know exactly what this produces. It doesn't name or contrast itself against any sibling (histor_check, warden_scan, x402_check), so differentiation is left to inference.

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?

"Send a tools/list or name a server HISTOR observes" tells the agent the two accepted input paths, which is real invocation guidance. However it never says when to reach for this tool versus the sibling checks, nor what happens if neither input is supplied (both parameters are optional).

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