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

With no annotations, the description carries the full burden. It discloses the deterministic nature ('Deterministically validates'), describes the return (a boolean status and a list of missing keys), and explicitly delimits what it does not do (regex validation, deep recursive casting), which prevents incorrect assumptions. It doesn't mention side effects, but validation implies non-mutating behavior.

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, no filler. The purpose is stated first, followed directly by usage guidance and exclusions. Every word carries weight.

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 tool with two required parameters, no output schema, and no similar siblings, the description covers the essential context: what it validates, how it returns results, and its limitations. It could mention error handling, but that's not required for correct invocation.

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 both parameters with descriptions and an example, so the description adds little beyond labeling it a 'reference schema dictionary'. With 100% schema coverage, the baseline is 3, and this description does not meaningfully augment the schema's clarity.

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 states a specific verb (validates), a resource (target JSON payload), and the precise scope (contains all mandatory keys from a reference schema dictionary). It distinguishes itself from other tools by explicitly saying it is not for regex string validation or deep recursive type casting.

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?

It provides explicit guidance on when to use ('Use when verifying payload structure before downstream processing') and states clear exclusions ('Do not use for regex string validation or deep recursive type casting'). While it doesn't name a specific sibling alternative, it gives enough context to avoid misuse.

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