List legacy U2F security keys enrolled to a user, with pagination controls, while never exposing private key material.
List the legacy U2F security keys enrolled to a user. Never returns private key material.
| Name | Required | Description | Default |
|---|---|---|---|
| limit | No | Number of items per page (Duo default/max vary by endpoint). | |
| offset | No | Offset into the result set, for paging past the first page. | |
| userId | Yes | Duo user_id. |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It does usefully disclose that private key material is never returned, which is a meaningful behavioral guarantee. However, it does not mention authentication requirements, error behavior, or pagination semantics beyond what the schema already implies.
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 one short sentence that front-loads the core purpose and adds a valuable safety note. Every word earns its place, and there is no redundant filler.
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-only list operation with fully documented parameters, the description is nearly complete. It covers the key behavioral guarantee (no private key material) and the resource scope, though it lacks an explicit return-value shape or edge-case details in the absence of an output schema.
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 schema already documents all three parameters clearly. The description adds little beyond restating the user-scoped nature of the listing ('enrolled to a user'), so it meets the baseline without adding significant new meaning.
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 uses a specific verb and resource: 'List the legacy U2F security keys enrolled to a user.' It clearly distinguishes this from similar sibling tools like webauthn_credentials and hardware tokens by specifying 'legacy U2F' and 'enrolled to a user.'
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 implies when to use the tool through its purpose, but it does not explicitly state when to choose this over sibling tools such as duo_list_user_webauthn_credentials or duo_list_user_tokens. There is no direct when-to-use or when-not-to-use guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.