Server info & capability catalog

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

Annotations already declare readOnlyHint/idempotentHint and destructiveHint=false, so safety needs little restating. The description adds genuinely non-obvious behavior: which backends are live, whether REST credentials are configured, the effective tailnet, and the exact reason a tool is unavailable (risk_gated vs. needs_credentials) with the environment variables that resolve each case.

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?

Dense but front-loaded: the report contents come first, the "use when missing" trigger follows, and the closing "Read-only" is a one-word reinforcement of the annotations. It is a single long sentence chain, so readability could be improved, but no sentence is wasted.

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 no parameters, no output schema, and annotations covering the safety profile, the description still enumerates exactly what the response contains (version, backends, tailnet, risk level, per-tool availability plus cause) and what the agent should do with each cause. Nothing needed to invoke or interpret this tool 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?

The tool takes zero parameters, so the baseline is 4 and there is no schema semantics to augment or omit.

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 (report) and a precise resource set: server version, live backends, effective tailnet, risk level, and a per-tool availability catalog. This is clearly distinguishable from diagnostic siblings like tailscale_status, tailscale_version or tailscale_whoami, which report tailnet state rather than server/tool-catalog state.

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?

"Use this when a tool you expected is missing" gives an explicit trigger condition, and the description enumerates the two remediation branches (risk gating vs. credentials) so the agent knows this is the routing tool for absent capabilities. No alternative tool is named for that job, so it stops short of full when/when-not/alternatives coverage.

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