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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the description's job is to add beyond these. It adds critical behavioral details: the tool never raises a protocol error on invalid input (returns a structured error object), it reaches out over the network, it is safe to retry after correcting input, and the output includes a permanent shareable report URL. There is no contradiction with annotations.

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 well-structured with clear paragraphs: purpose, core use case, example output, sibling differentiation, and error behavior. Every sentence is non-redundant and adds unique value. It is front-loaded with the key verb and scope.

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 has 1 simple parameter, rich annotations, and an output schema (indicated by context signals), the description covers everything: purpose, input handling, output structure, error behavior, idempotency, and safety guarantees. There are no gaps for an agent to misinterpret.

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%, so the baseline is 3. The description adds value by showing typical input/output examples and the error handling pattern, which clarifies how the domain parameter is used. It also adds the nuance that a full URL is accepted and reduced to its host. However, it does not add entirely new semantics beyond what the schema already documents.

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 uses a specific verb ('Score') and clearly identifies the resource ('a public domain against 21 agent-readiness checks'). It also distinguishes itself from siblings by name in the usage guidelines section, and the title reinforces the purpose. There is no ambiguity about what the tool does.

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 states when to use the tool ('when you need to know whether an autonomous agent can discover, read, use or pay a website') and provides two specific exclusions by naming sibling tools ('Not for auditing an MCP client configuration (audit_mcp_config) and not for scanning text for injection (injection_scan)'). It also clarifies what it does differently ('this one reaches out over the network'). This is exemplary guidance.

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