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

With no annotations provided, the description carries the full burden. It discloses that the tool is 'Free' and details the returned information (capability, version, cache tier, price paid, on-chain settlement). The verb 'look up' implies a read-only operation, but it does not explicitly state side-effect-freedom or require authentication. Still, it provides useful behavioral context beyond the schema.

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?

Two sentences, front-loaded with 'Free' and the core purpose. Every sentence contributes value – the first describes what it does, the second specifies when to use it. No wasted words.

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 single-parameter lookup tool with no output schema, the description adequately lists the result fields (capability, version, cache tier, list price, credit, paid price, on-chain settlement). It fully explains the tool's purpose and context. Minor gaps like not-found behavior do not significantly impede understanding.

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 already covers the single parameter 'invocationId' with description 'Invocation id from a receiptUrl.' The tool description does not add further meaning about the parameter beyond referencing 'settled invocation' in the purpose. Baseline 3 is appropriate since schema coverage is 100%.

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 'Look up what a settled invocation actually charged' – a specific verb and resource. It clearly distinguishes this tool from siblings like tereno_price (for quotes) and tereno_catalog (for catalog data) by focusing on settled receipts/billing verification.

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 explicitly states the intended use: 'Use it to check that a call you or another agent paid for was billed the way it was quoted.' This gives a clear when-to-use signal. It does not explicitly mention when not to use it or name alternatives, but the use case is specific and actionable.

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