Look up a ZIP

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

Annotations already indicate read-only and open-world hints. The description adds valuable behavioral details: the exclusion of ZIPs with fewer than 100 returns and the specific data returned (state, counts, tax year). It does not contradict annotations and enhances understanding beyond them.

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 concise and front-loaded with the core purpose. Every sentence adds value: the ZIP format, the use case, and the exclusion rule. No redundancy or irrelevant 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 simple single-parameter lookup with an output schema, the description covers the essential context: what it does, when to use it, and key constraints. It does not describe the not-found behavior, but the output schema likely handles that, and the annotations cover safety.

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?

With 0% schema description coverage, the description compensates by defining 'zip_code' as a 5-digit US ZIP and noting the exclusion threshold. It adds practical meaning beyond the schema's basic property definition, though it could specify validation rules more explicitly.

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 clearly states the tool's purpose: to confirm a ZIP has SOI data and return counts. It uses specific verbs and identifies the resource (ZIP), and distinguishes itself from siblings by positioning as a validation first call.

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 recommends this as a 'good first call' before requesting more detail, giving clear usage context. It does not name alternative tools or provide when-not-to-use scenarios, but the context is sufficient for a simple lookup tool.

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