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

Annotations already cover the safety profile (readOnly=true, idempotent=true, destructive=false), so the description adds the valuable behavioral context: the result is a summary, not the full record; it names the included fields (name, operator, location, status, market) and the excluded ones (capacity MW, coordinates). The return-shape detail partially duplicates what the output schema provides, so not a full 5, but the limitation disclosure is genuinely 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?

Three sentences, each earning its place: purpose, return shape and content, then explicit alternative routing. Front-loaded with the primary action. No fluff; the OpenAI-format parenthetical adds useful compatibility context rather than noise.

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 single-parameter, schema-covered, output-schema-rich read tool, the description is complete: it states what the input must be, what the output contains, what it does not contain, and where to go for the missing detail. Nothing an agent needs to call it correctly is unstated.

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% — the id parameter already says it is 'A facility id/slug from a prior search result, e.g. equinix-dc1-ashburg'. The description only reinforces the same provenance ('an id returned by the search tool') without adding new meaning beyond the schema. Baseline 3 is correct.

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 ('Fetch a DC Hub record') with explicit provenance ('for an id returned by the search tool'), and clarifies exactly what kind of record it returns (a citable public summary). It differentiates itself from get_facility by describing the record's scope (summary vs full structured specs), so an agent can tell siblings apart.

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?

Explicitly wires the tool into a workflow ('for an id returned by the search tool') and names the alternative ('For full structured specs... use get_facility or open the url') with the condition that selects it. An agent knows when to call fetch and when to route elsewhere without inference.

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