Explain available tools

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, closed-world, so the safety profile is covered. The description adds genuine behavioral context beyond that: tools can be withheld by configuration, the fix is usually an environment variable, and it is 'always available regardless of filters.' It stops short of describing output shape, but that is largely implicit in the outcome enumeration.

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?

Front-loaded with the core directive ('Call this FIRST when...') before the parameter and no-argument behaviors. Dense and mostly waste-free, though the middle clause is somewhat run-on and could be tightened.

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?

There is no output schema, so the description must convey what comes back; it does so by enumerating the three distinguishable outcomes and the no-argument group listing with environment-change details. For a single-optional-param introspection tool, nothing an agent needs to call it correctly is missing.

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 coverage is 100% and the parameter is already documented, so baseline is 3. The description goes further by explaining what the answer to `toolName` actually distinguishes (no such tool vs. group not loaded vs. writes withheld), adding semantic meaning beyond the schema's 'omit to list every group.'

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?

States a specific verb and object ('Explain which of this server's tools are available and why'), a capability that is clearly distinct from every sibling, which are all Tailscale API operations. An agent can immediately tell this is a meta/introspection tool rather than an API call.

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?

Explicitly states when to call it: 'Call this FIRST when a Tailscale tool you expected is missing, instead of assuming the capability does not exist.' It also gives the fallback reasoning for each outcome (find another approach vs. ask the operator to enable), covering both when-to-use and when-not-to-work-around.

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