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

With no annotations provided, the description carries the full burden of behavioral disclosure. It does disclose the status filter (scheduled, not yet sent), which is useful scoping behavior, but it does not explicitly state that this is a read-only operation, nor does it describe the output structure or any limits. For a list tool, this is adequate but lacks the richer detail that annotations would normally provide.

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 two sentences with no fluff. The first sentence front-loads the verb 'List' and the resource, and the second sentence provides practical use cases. Every word earns its place, maintaining brevity without sacrificing key details.

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 tool with zero parameters and no output schema, the description covers the key selection criteria (status filter) and use cases. However, it does not specify what the returned objects contain (e.g., message IDs, content, send time), which is a gap given the absence of an output schema. An agent might need that detail to invoke the tool correctly in a follow-up action like cancellation.

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 input schema has zero parameters, so there is nothing to explain. The description adds context about what the list contains (user's pending scheduled SMS messages), which complements the empty schema. Per the rubric, 0 parameters gets a baseline of 4, and the description does not detract from that.

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 starts with a specific verb and resource: 'List the user's pending scheduled SMS messages.' It clarifies the status filter (status='scheduled', not yet sent), which distinguishes it from siblings like sms_send_scheduled (schedules) and sms_cancel_scheduled (cancels). The 'finding a message id to cancel' phrase further connects it to the cancellation workflow, leaving no ambiguity about its role.

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 use cases: 'showing the user what's queued up or finding a message id to cancel.' This indicates when to use the tool but does not explicitly name alternatives or state when not to use it. The context is clear enough for an agent to select it over siblings, though it stops short of full when-not guidance.

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