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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false. The description adds extra context: 'Every call is read-only and idempotent' (consistent) and 'on invalid, missing, or malformed input this tool never raises a protocol error — it returns {"error": ...}' which is valuable behavioral detail not present in annotations. No contradictions.

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 front-loaded with purpose, then gives an example, then usage guidelines, then error behavior. It is fairly concise but contains minor extras like 'PREMIUM (license)' which adds little. Overall well-structured and each sentence adds value, though slight trimming could improve conciseness.

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?

Given the tool has an output schema (as indicated by context signals), the description does not need to fully describe return values. It provides an example output, error behavior, usage boundaries, and input requirements. For a simple two-parameter tool, this is highly complete and leaves no significant gaps.

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 description coverage is 100% and both parameters are well-described in the schema (price must be >0, discounts_pct is an array with examples). The description's example input/output reinforces but does not add new semantic meaning beyond the schema. Baseline 3 is appropriate as description adds context via example but no new constraints or clarifications.

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 explicitly states the tool compares sequential vs additive discount stacking, which is a specific verb+resource. It distinguishes itself from sibling tools like invoice_total by noting 'Not for a single discount inside an invoice (invoice_total)' and mentions other siblings implicitly through usage guidance.

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?

Clearly says 'Use when more than one discount applies and the order changes the answer' and 'Not for a single discount inside an invoice (invoice_total)'. This gives explicit when-to-use and when-not-to-use, with a named alternative. Also provides error handling guidance: safe to retry after correcting input.

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