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

Annotations already indicate the tool is not read-only and not destructive. The description adds the behavioral context that this is a legacy alias to buy_gas, which is useful but does not disclose specific side effects such as crediting the account or deducting balance. Given the annotations cover the safety profile, this is adequate but not rich.

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 description is a single sentence that immediately states the tool's role as an alias and its legacy status, followed by a clear preference instruction. Every word is informative and the structure is optimally front-loaded.

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?

The tool is a simple alias with one parameter and no output schema. The description adequately redirects to buy_gas and explains the legacy nature, which is sufficient for an agent to understand the tool's role. It could benefit from specifying the underlying purchase behavior, but the sibling pointer mitigates that.

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 description provides no information about the packId parameter, and schema description coverage is 0%. Although the schema's enum values (starter, builder, fleet) are self-explanatory, the description fails to compensate for the lack of parameter documentation.

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 clearly identifies the tool as a legacy alias for buy_gas, which distinguishes it from the sibling tool buy_gas. However, it does not explicitly describe the underlying operation (e.g., 'purchases credits'), relying on the tool name and buy_gas's own description for full meaning.

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 instruction 'Prefer buy_gas' provides explicit guidance that this tool should be avoided in favor of buy_gas, making the usage context very clear. It does not specify when to use this legacy alias, but the preference alone is sufficient.

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