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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the bar is lower, but the description adds meaningful context beyond them: it discloses the result fields (up/down, HTTP status, response time), states the parallelism behavior, and explicitly notes 'Free, no key.' It does not cover timeout/error behavior or redirect handling, but the key operational facts are present.

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 action, scope, and return values. Every clause adds useful information with no filler.

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 simple read-only tool with one parameter and no output schema, the description supplies the essential return-value summary and access requirement. It falls short only on edge-case behavior such as invalid URLs, timeouts, or partial failures.

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 single 'urls' parameter is partly clarified by the description ('up to 10 URLs', checked in parallel), but the schema already enforces maxItems=10 and the array type. The description does not add URL format requirements or clarify invalid-input behavior, so it adds only marginal meaning beyond 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?

The description states a specific verb and resource ('Check ... URLs') plus a clear scope ('up to 10 URLs in parallel'), which distinguishes it from the singular sibling check_website. An agent can tell immediately that this is the batch URL-checking tool.

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 batch limit and parallel checking imply usage for checking multiple URLs at once, but the description never explicitly says when to use this instead of check_website or start_uptime_monitor. No exclusions or prerequisites are stated.

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