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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, and the description adds value beyond them: the score is a DERIVED convenience not a DC Hub grade, users should cite underlying counts when load-bearing, and records are PeeringDB's refreshed on read. This is exactly the kind of provenance and trust caveat annotations cannot express.

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?

Front-loaded with the core purpose and mode switch, then fields, then alternatives. The Ashburn numeric example is somewhat verbose for a description, but it concretely anchors expected output shape and is not padding.

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 zero-required-param, dual-mode read tool with an output schema, the description covers both modes, the meaning of the derived score, data provenance and refresh behavior, and sibling routing. An agent has everything needed to select and invoke it correctly.

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 baseline is 3, but the description adds mode-switching semantics the schema only implies: passing lat+lon selects the peering-profile response while omitting coordinates selects the IXP directory. It does not explain the alias set (lng/latitude/longitude) or the limit parameter, but those are documented in the schema.

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 ('IX/IXP and peering density for a site, from PeeringDB') and explicitly contrasts itself with adjacent capabilities (fiber route geometry, fiber readiness, metro fiber, subsea cables). An agent can distinguish it from every named sibling without opening a schema.

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?

Gives explicit when-to-use (lat+lon for peering profile, omit for IXP directory), concrete example calls, sample questions it answers, and a clear do-not-use list pointing to four alternatives. Nothing is left to inference.

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