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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds one useful trait not in annotations – that no authentication is required – but nothing about rate limits, caching, or freshness, so it stays at the baseline band.

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 short sentences, zero filler, with the core return value front-loaded before the access note. Every sentence earns its place.

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 parameterless lookup with no output schema, the description tells the agent what comes back (destination and dial code) plus the no-auth constraint, and annotations cover safety. Only the routing gap versus similar number-related siblings keeps it just short of full completeness.

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 schema has zero parameters, and the rubric sets a baseline of 4 for parameterless tools. There is no parameter surface for the description to clarify, so this dimension is essentially satisfied by definition.

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 ('Returns') and resource ('UK shared Always-forward destination and the dial code'), which is distinct enough to identify the output. It does not explicitly distinguish itself from similar siblings like get_forwarding or quote_number, so it does not reach the top band.

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 only usage-flavored note is 'No sign-in', which is really an access trait moved into behavioral territory. There is no guidance on when to use this versus get_forwarding, quote_number, or search_numbers, and no exclusions or prerequisites.

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