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

Annotations already flag destructiveHint=true, openWorldHint=true, and idempotentHint=false; the description adds genuinely new behavioral facts — a hard approval gate and a 1 SMS credit cost. It still doesn't say what happens if delivery fails or whether credits are refunded, but the approval/cost disclosure is real added value.

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?

Three short sentences, zero filler, with the action stated first and the safety/cost constraints following. Every sentence carries distinct information.

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 destructive, open-world mutation with no output schema, the description covers the critical agent-facing risks: approval requirement, the confirm gate, and credit cost. It leaves failure modes and delivery confirmation implicit, which is a minor gap given the fully documented schema.

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?

Schema coverage is 100%, so the baseline is 3, but the description goes beyond the schema by framing message and owner_id as values that must be surfaced to the user and approved verbatim before confirm can be set. That reinforces the confirm parameter's const:true semantics with workflow meaning rather than restating the field list.

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 and resource ('Text an owner') plus the sending channel ('from the user's Spur number'), which cleanly separates it from siblings like spur_create_sms_template, spur_draft_message, and spur_get_sms_conversation. An agent can identify this as the actual send action without opening the schema.

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?

Gives a clear when-to-use prerequisite: show the exact message and recipient, obtain approval, then call with confirm=true. It does not name alternatives (e.g., draft first via spur_draft_message, or reuse a spur_create_sms_template), so it stops short of full routing guidance.

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