check_sms_credit

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

The readOnlyHint annotation already conveys this is a safe read operation. The description adds no extra behavioral context such as authentication requirements, rate limits, or caching behavior. However, for a simple zero-parameter balance check, the annotation covers the main safety concern, so the description does not need to add much.

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 is concise and front-loaded with the action and resource. Every word earns its place, with no unnecessary fluff or repetition.

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?

Given the tool's simplicity (zero parameters, no output schema, read-only annotation), the description is adequately complete. It identifies the specific service (ThaiBulkSMS) and the resource (SMS credit). While it doesn't describe the return format, that is not critical for a simple balance check and is implied.

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 description does not need to explain any. Per the rubric, a zero-parameter tool is a baseline 4, and the description clearly specifies what is being checked, which is sufficient given 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?

The description clearly states the tool checks the remaining SMS credit balance on ThaiBulkSMS, using a specific verb ('Check') and resource ('SMS credit balance'). It distinguishes from sibling check_email_credit by specifying SMS, making the purpose unambiguous.

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 description implies the tool is used to monitor SMS credit, especially before sending messages, but does not explicitly state when to use it versus alternatives like check_email_credit. There is no mention of exclusions or conditions, so usage guidance is only implied.

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