filoo_list_usernames

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

The description discloses the purpose and output (list of usernames with primary flag) and adds context about the naming scheme (filoo.app/{username}/{slug}). Since there are no annotations, the description carries the full burden. The tool has no side effects and is a simple read operation, so the description is sufficiently transparent for its simplicity, though it could explicitly mention that it is read-only and requires 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?

Two sentences: the first describes the core functionality concisely, and the second adds valuable context about the naming convention and purpose. Every sentence is meaningful and there is no 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?

With zero parameters, no output schema, and a simple list operation, the description is complete. It tells what is returned (usernames + primary flag) and why an agent would use it (to discover namespaces for publishing). No additional information is needed.

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?

The tool has zero parameters, so the input schema is fully covered (100%). The description does not need to explain parameters. The baseline for 0 parameters is 4, and the description adds no extra parameter info, which is acceptable.

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 clearly states 'List every username the authenticated user owns on filoo, along with which one is primary.' It explains the broader context of short links living under a username (filoo.app/{username}/{slug}) and that this is the canonical way to discover namespaces for publishing. This distinguishes it from sibling tools like filoo_list_links which list links, not usernames.

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 explicitly says 'this is the canonical way for an agent to discover what namespaces it can publish into,' which indicates when to use the tool (before creating a link). It doesn't specify when not to use it or provide explicit alternatives, but the context is clear enough for an AI agent to infer its appropriate usage.

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