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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds useful context about what the call yields (providers, their networks, per-type plan counts), which is more than the annotations convey, though pagination/result-size behavior is unstated.

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, zero waste: the first delivers scope and return content, the second delivers the routing rule. Both are front-loaded and easy to scan.

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?

Output schema exists so return values needn't be enumerated, and the description still summarizes them well. The only real hole is the undocumented optional plan_type filter, which keeps this just short of fully complete.

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?

There is one parameter (plan_type, an enum) with 0% schema description coverage, and the description never mentions it. The stated return ('how many plans of each type') strongly implies the filter changes those counts, but the agent is left to infer this entirely on its own.

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?

Specific verb+resource ('List the telco providers') plus the returned fields (network, plan counts per type), which no sibling offers. An agent can distinguish this from compare_plans, get_plan and search_plans without opening any 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?

Explicitly states the use case: 'resolve a provider name to its slug before calling search_plans or get_plan', naming both downstream alternatives. It lacks a when-not-to-use clause, but the routing guidance is clear and actionable.

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