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

Annotations indicate readOnlyHint=false and openWorldHint=true, but the description adds crucial behavioral context: the key is bound to one number and cannot message anyone else. This constraint is not visible in the schema or annotations and meaningfully affects usage, so the description earns credit beyond annotations.

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 three sentences long, front-loads the core purpose, then adds a constraint and usage examples. Every sentence earns its place with no fluff or repetition of the title or schema.

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 a single parameter, full schema coverage, and no output schema, the description provides complete context: what it does, who receives it, when to use it, and how to phrase the message. No gaps remain for the agent to guess.

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?

Input schema covers 100% of parameters and the 'message' parameter already has rich description. The tool description adds extra guidance on message composition ('Say plainly whether anything needs them, and if something does, offer the next decision'), which goes beyond the schema's lock-screen advice. This pushes the score above the baseline of 3.

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 uses a specific verb-resource pair ('Send a text message to the phone number that owns this SelfPing API key') and clearly distinguishes itself by explicitly stating there is no recipient argument. This makes the tool's purpose unambiguous and well-scoped.

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 provides explicit 'when to use' guidance: 'Use this to notify the operator when a long job finishes, a deploy completes, or an error fires.' It also gives style guidance for the message ('Say plainly whether anything needs them...'), which is valuable for correct invocation.

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