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

Annotations only indicate readOnlyHint=false and destructiveHint=false, so the description adds useful context by naming the authentication method (NPKI certificate) and noting that it returns a session credential. However, it does not disclose side effects such as creating a server-side session or invalidating prior sessions.

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 short sentences with no filler. The critical 'call first' instruction is front-loaded, and the authentication method and return value are stated efficiently.

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 login tool with zero required parameters and no output schema, the description is sufficiently complete: it explains when to call it, how authentication works, and what is returned. It could add session lifetime or propagation details, but these are not essential for the agent to invoke the tool correctly.

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 single optional parameter account_link_id is fully documented in the schema with 100% coverage, including guidance about when to provide it explicitly. The description adds no parameter-level detail, so the schema carries the burden as expected.

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: 'Login to Hometax via NPKI certificate' and explicitly says to call it FIRST before any other provider tool. This clearly distinguishes it from sibling tools like hometax__session__user_info and other provider login tools.

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 gives clear usage context: 'Call this FIRST before any other tool for this provider.' It does not explicitly state when not to use it or mention alternatives for already-active sessions, but the ordering directive is strong and actionable.

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