Endpoint Reachability Check

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

Annotations already provide readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true. The description adds further behavioral context by explaining it's unauthenticated, reports HTTP status, content type, elapsed time, auth/rate-limit signals, and a response sample, and notes that success only proves basic reachability at fetch time. This goes beyond annotations without contradicting them.

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 description is three well-structured sentences. The first sentence states purpose and when to use, the second explains what the tool reports, and the third provides a strong 'do not use' warning. Every sentence is essential and adds value, with no wasted words.

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?

Given the tool's simplicity (one parameter and an output schema), the description covers purpose, usage guidelines, behavioral details, and limitations comprehensively. It tells the agent when to use, what it returns, and what not to expect, making it fully sufficient for correct invocation.

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 input schema has one parameter (url) with 100% description coverage. The description adds extra information beyond the schema by specifying that bare domains are accepted and normalized to https:// automatically, which helps the agent understand how to provide the URL.

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 clearly states that the tool performs a live, unauthenticated fetch against a public URL or API endpoint, and specifies its purpose: to check reachability before recommending, documenting, or building on top of an endpoint. It distinguishes from siblings by focusing on simple reachability questions.

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 the tool (before recommending, documenting, or building on top) and provides clear alternatives: it should not be used for authenticated flows, POST side effects, JavaScript execution, or deeper business logic. This gives the agent explicit guidance on when not to use it.

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