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

The description adds significant behavioral context beyond the annotations: it explicitly states the tool never returns ciphertext, lists the metadata fields returned (alg, size, timestamps), explains that updated_at serves as the version for conditional stores, and discloses the exact cost and payment mechanism. It does not contradict the readOnlyHint or idempotentHint annotations.

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?

Three sentences, each earning its place: the first states the core purpose, the second highlights the security boundary and alternative, and the third gives usage context and cost. Information is front-loaded and there is 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 description covers purpose, constraints, alternative routing, practical usage ('updated_at ... as if_match'), and cost/payment options. Combined with the output schema and annotations, the agent has everything needed to decide when to call this tool and how to interpret its response.

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 adds little parameter-specific meaning beyond the schema; it references credit tokens and namespace context but does not clarify any parameter beyond what the schema already states. This is adequate but does not go beyond the structured fields.

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: 'List the keys held in a namespace with their metadata'. It distinguishes itself from siblings by explicitly saying 'Never returns ciphertext — use vault_retrieve for that.' This makes it immediately clear what the tool does and how it differs from related 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?

The description gives explicit guidance: 'Use this when you have stored secrets and need to know what is there.' It also names the alternative tool for retrieval of secret values ('use vault_retrieve for that') and provides a conditional path for free credit via credits_trial. This is strong, actionable usage guidance.

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