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

Annotations already indicate readOnlyHint and idempotentHint, and the description adds meaningful behavioral context: it returns no ciphertext, requires the namespace_token, costs a specific amount, and explains the two payment paths. This goes well beyond the structured annotations, particularly around cost and authentication.

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: the core behavior appears first, followed by the essential prerequisite and cost information. Every sentence adds necessary operational detail without redundancy or fluff.

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 output schema exists, return values need not be described. The description covers the key behavioral, authentication, and cost details needed to invoke the tool. It misses only explicit sibling differentiation for when to choose this over vault_retrieve, so it is nearly complete but not perfectly so.

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%, so the baseline is 3. The description reinforces the namespace_token requirement and references credit_token indirectly, but adds little semantic detail beyond what the schema already provides. This is adequate but not exceptional.

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 and resource: 'Check for a key' and explicitly notes it does so 'without returning its ciphertext,' making it clearly distinct from vault_retrieve. The title reinforces the existence-testing purpose. It is immediately obvious what this tool does.

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 conveys clear context around prerequisites and cost, but does not explicitly name alternatives such as vault_retrieve or state when an agent should prefer this tool over them. The phrase 'without returning its ciphertext' implies an existence-only use case, but this is not made explicit enough for definitive routing.

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