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

The description's core action is a paid purchase — 'Pay for gigabytes of traffic', 'after payment', 'Pay per pack in stablecoins' — while the annotations assert readOnlyHint=true and destructiveHint=false. Calling this tool spends funds and provisions a 90-day pack, which is a side-effecting, non-idempotent operation (consistent with idempotentHint=false, but inconsistent with readOnlyHint=true). An agent trusting the annotation would wrongly assume calling it repeatedly is free and harmless.

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 definition is front-loaded ('Residential proxy for AI agents') and each sentence carries product information. It is slightly redundant on payment, mentioned twice ('Pay for gigabytes of traffic' and 'Pay per pack in stablecoins'), which could be consolidated into one sentence.

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?

With no output schema, the description usefully covers what is returned (host, port, username, password), how long the pack lasts, how exits are selected, and how payment is made. Gaps remain around the charging behavior per call and failure/refund handling, but for a two-parameter tool it is largely 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?

Schema description coverage is 100%, so the baseline is 3. The description adds conceptual value by explaining that country is a default exit that the username can override per connection and that IP rotation vs. sticky sessions is configurable — but the 'session tag' mechanism is never tied to a parameter or a username syntax, and the gb semantics rest entirely on the 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?

The description gives a concrete verb+resource: purchase a residential proxy pack and receive a login (host, port, username, password) usable with curl, browsers, or HTTP clients. It is unambiguous what the tool does. It does not, however, differentiate itself from the sibling `fetch` (presumably the tool that routes traffic through the purchased proxy), which the rubric requires for a 5.

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?

Usage is implied via the service context (use the credentials with curl/browser/HTTP clients, rotate per connection or hold a sticky session, pack lasts 90 days) rather than stated as when-to-use. There is no explicit guidance on when to call this versus `fetch`, nor on prerequisites such as needing an agent wallet/stablecoin balance before calling.

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