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

The readOnlyHint annotation already signals a safe read operation. The description adds valuable context by specifying 'subnet routes a device advertises and which are enabled', clarifying the scope of the listing. The REST GET endpoint reinforces read-only behavior, though no additional details like authentication or response format are provided.

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 concise sentences: the first states the core functionality, the second cites the REST endpoint. No redundant or filler content; each sentence carries meaningful information.

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 one-parameter read-only list tool with a clear schema, the description covers the purpose and partially describes the output (advertised vs enabled routes). No output schema exists, so the description could have mentioned the return format more explicitly, but it is sufficiently complete given the tool's simplicity.

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 schema fully describes the only parameter (deviceId) with 'The device id.' The description does not elaborate on the parameter, but since schema coverage is 100%, the baseline of 3 applies. No extra meaning is added beyond confirming the device context.

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?

Description clearly states 'List the subnet routes a device advertises and which are enabled', specifying the verb (list) and resource (subnet routes of a device). It distinguishes from siblings like tailscale_set_device_routes (which modifies routes) and tailscale_list_devices (which lists devices). The REST endpoint is also provided for further clarity.

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 usage context: use this tool to list routes, and the presence of tailscale_set_device_routes in siblings hints at the alternative. However, no explicit when-to-use or when-not-to-use guidance is given, so it remains at baseline implied usage.

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