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

Annotations already mark the tool as read-only; the description adds context by clarifying that this is an overview resource and explicitly excludes city-dependent rates. It also says the slug is the starting point for other tools. No contradiction with annotations, and the added scope boundary is useful.

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 dense sentences with no filler. The first front-loads the resource and its content; the second gives the practical purpose and points to alternatives. Every clause 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 zero-parameter, no-output-schema list tool, the description names the returned attributes, states why the agent should start here (to get slugs), and routes to the correct tools for rates. Nothing needed for correct invocation is missing.

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 tool has zero parameters, so the schema provides no semantic burden and the baseline for 0-param tools is 4. The description explains what the output contains, which is the relevant semantic information here.

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 and resource: list all delivery services in CourierHUB's Russian network, and enumerates the content dimensions (what can be transported, pay frequency, schedule, rating, cities). The phrase 'Начните отсюда, чтобы узнать slug сервиса' clearly frames its role and distinguishes it from singular get_service and rate-specific siblings.

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 says 'Начните отсюда' for getting slugs used by other tools, and tells the agent that rates are not here, redirecting to get_city_rates and calculate_income. This is direct when-to-use / when-not-to-use guidance with named alternatives.

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