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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, and the description reinforces them ('never charges and never writes external state') plus adds gateway-specific behavior about what is executable versus merely discoverable. The added context is genuinely useful, but it largely restates the safety profile the annotations already carry.

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 tight sentences, each front-loaded with the core purpose first, then return shape, then safety and gateway constraints. No filler or repeated 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?

With no output schema, the description compensates by naming the return shape (candidate set with evidence-grounded match reasons, price, latency, status), and it explains the hosted-gateway invocation constraint. Nothing essential to correct selection or invocation is missing.

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 parameter meaning is already fully documented in the schema. The description only gestures at price and 'free or pay-per-use' filtering without explaining how limit, media_type, or payment_modes behave, so the baseline 3 applies.

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?

Names a specific verb and resource ('Find an external service') and scopes it to outcomes current tools cannot handle, which cleanly separates it from invoke_capability (execution) and get_capability (detail lookup). An agent can tell what this tool produces 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?

The conditional 'complete an outcome your current tools cannot' gives clear when-to-use guidance, and the note that writing capabilities are marked invocable_here:false implies the follow-up path. It stops short of naming sibling alternatives (get_capability, invoke_capability) explicitly.

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