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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive, so the 'Behavior: read-only' line is largely redundant. However, the description adds a genuinely useful operational precondition not captured in any structured field: it requires PAYWALL_API_KEY, which tells the agent about an auth dependency before invocation.

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?

Front-loaded with the bracketed domain tag, then purpose, then usage, then behavior — a clean information hierarchy. The closing 'Behavior: read-only' sentence duplicates the annotation and is the one line that does not fully earn 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, non-destructive list tool with no output schema, the description covers purpose, the auth prerequisite, the returned data ('routes and their prices'), and the correct alternative. Only minor gaps remain, such as pagination or the exact fields per route, which are low stakes here.

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 takes zero parameters, so there is no parameter semantics burden and the baseline of 4 applies. Nothing in the description conflicts with the empty 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?

States a specific verb and resource ('List your paywalled routes') and immediately scopes it with the price data it returns. It also names the sibling it is not (paywall_list_settlements), so an agent can distinguish it from the settlement tooling without opening a 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 gives the triggering condition ('Use when you want your paywalled routes and their prices') and an exclusion with a named alternative ('Not for earnings (use paywall_list_settlements)'). That is the when-to-use / when-not-to-use / alternative triad.

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