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

No annotations are provided, so the description carries the full burden. It discloses that the tool returns immediately, requires no authentication, is not metered, and is safe for polling. This is strong behavioral disclosure for a health-check tool. It doesn't mention the exact response shape, but the output schema exists and the behavior is simple enough that this is a minor gap.

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, front-loaded with the core behavior ('Returns immediately if the API is up'), followed by the key operational guarantees. Every word earns its place; no fluff or repetition of schema information.

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-parameter health-check tool with an output schema, the description is complete. It covers behavior, auth, metering, and safe usage contexts. An agent has everything it needs to decide when to call this tool and what to expect.

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?

The tool has zero parameters, so there is no parameter semantics burden. The description adds value by explaining the operational context (no auth, not metered) which is more useful than any parameter documentation would be. Baseline 4 for zero params is appropriate.

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 specific verb ('Returns') and resource ('API up' status), and clearly distinguishes this from the sibling 'ping' tool by adding the 'head' semantics — immediate return, no auth, not metered. An agent can tell exactly what this tool does without opening the 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?

The description explicitly says when to use it: 'safe to poll from a load balancer, uptime monitor, or status dashboard without affecting your usage.' It also implicitly excludes use cases requiring authentication or metered operations. This is clear context with no ambiguity.

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