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

Annotations already establish readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: it returns billing implications, retryability, retry delay, and a recommended agent action, which tells the agent why the call is worth making.

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 tight sentences, front-loaded with the action and catalog, followed by the return payload. No filler or redundancy.

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?

The output schema covers return values, so the description need not enumerate them, and the read-only nature is annotated. The one omission is that with zero required parameters it never says whether code, reason, or http_status must be supplied (or whether multiple can be combined), which an agent needs to invoke correctly.

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% and each parameter carries its own description with examples, so the schema does the heavy lifting. The description only restates the lookup keys and adds nothing about how to combine them or that at least one is needed; 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?

States a specific verb ('Lookup') and resource ('official error reference catalog') and names the three lookup keys (error code, reason, HTTP status), which clearly separates it from sibling doc/search/pricing tools.

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?

Usage is implied by the keys it accepts: call it when you have an error code, reason slug, or HTTP status to interpret. However, it never states when to prefer this over search_docs or read_doc, nor any exclusions, so guidance is only inferred.

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