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

Annotations cover the safety profile (non-read-only, non-destructive, non-open-world), so the bar is lower; the description adds genuinely useful context by stating it deducts balance (a financial side effect) and that credentials persist. It stops short of describing failure behavior, e.g. what happens with insufficient balance, so not a 5.

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 compact sentences, front-loaded with the core action and parenthetical qualification. Every clause earns its place with no filler.

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 two-parameter mutation with annotations and no output schema, the description covers action, scope, and the balance deduction. It could mention limits or failure conditions, but nothing critical to invoking it correctly 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?

Both parameters (proxy_id, traffic_gb) are fully documented in the schema at 100% coverage, so the baseline is 3. The description adds nothing about the parameter semantics beyond the schema, but it does not need to.

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 (adds) and resource (prepaid GB to an existing proxy), plus the useful reassurance that existing credentials continue to work. It does not explicitly contrast itself with the sibling buy_proxy, which also involves purchasing traffic, so a 4 rather than 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?

The word 'existing' implies this is for proxies already owned, which nudges an agent away from buy_proxy, but the description never states when to use this versus buy_proxy or attach_recovery. Usage is implied rather than guided.

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