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

Even with annotations indicating mutation and destructiveness, the description adds substantial non-obvious behavioral context: the service never sees plaintext, but stores key/namespace/alg/size in the clear; the namespace_token is shown only once and cannot be recovered; concurrent writes return 'precondition_failed' instead of silently overwriting; and each call costs $0.02 via x402. There is no contradiction with the 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?

The description is dense but every sentence carries essential operational or security information. It front-loads the core purpose and privacy caveat, then covers token handling, concurrency guards, and cost. There is no fluff or restatement of the title.

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 8 parameters, concurrency controls, a one-time token, security caveats, and payment requirements, the description covers all critical invocation facts. The output schema exists, so missing return-value details are acceptable. Nothing important for correct use is left unexplained.

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?

Input schema covers all 8 parameters at 100%, so the baseline is 3. The description adds meaningful value by explaining the namespace_token lifecycle, compare-and-swap semantics, and the client-side encryption requirement. Some details are redundant with schema descriptions, so a 4 rather than 5.

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: 'Store client-side encrypted data.' It clearly distinguishes this from sibling operations like vault_retrieve, vault_list, and vault_delete. The title reinforces the core action, leaving no ambiguity about what the 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 gives concrete usage guidance: the first store claims the namespace and returns a one-time namespace_token that must be saved, and it explains when to use if_match versus if_absent to avoid clobbering concurrent writes. It does not explicitly name alternative sibling tools or provide when-not-to-use guidance, which prevents a 5.

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