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

Annotations already declare readOnlyHint and idempotentHint, so the description doesn't need to restate that. It adds valuable behavioral context: the $0.02 cost on Base, the x402 payment requirement, the credit_token alternative, and the namespace_token prerequisite. It also clarifies this returns a ciphertext, not a decrypted secret.

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 with no fluff. The first sentence states the core action; the second covers prerequisites and cost, including a pointer to credits_trial. Every clause earns its place.

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 read tool with full schema coverage, an output schema, and idempotent/read-only annotations, the description is nearly complete. It covers cost, prerequisites, and payment alternatives. Missing details like error behavior are minor and the output schema likely covers return values.

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 description doesn't need to repeat parameter details. The description does add context about the payment flow and the credit_token alternative, but it doesn't explain individual parameters beyond what the schema already states. Baseline 3 is appropriate.

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 opens with a specific verb and resource: 'Retrieve a previously stored ciphertext.' This clearly distinguishes it from sibling tools like vault_list (list keys) and vault_exists (check existence). The phrase 'previously stored' also implies it is the counterpart to vault_store.

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 gives clear context for when to call it: to retrieve a stored ciphertext, and it specifies the required namespace_token and payment options. It does not explicitly name alternative tools or exclusion criteria, but the purpose is unambiguous enough that an agent can infer when it is appropriate.

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