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

With no annotations, the description carries the disclosure burden and usefully states that login stores a session cookie in hn_session_cookie. However, it omits important behavior around invalid credentials, existing sessions, cookie lifetime, security implications, and failure modes.

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?

The definition is two compact sentences with the core action front-loaded and the cookie-storage consequence immediately following. There is no redundant or filler language.

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 three-parameter authentication tool with no output schema and no annotations, the description gives enough context to call it: credentials are required and a session cookie is stored for later authenticated actions. It could be more complete by explaining session reuse and failure behavior, but the essential invocation context is present.

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 description mentions username and password, matching the two required parameters, but adds no syntax, format, or validation details beyond the schema. Because schema description coverage is 100%, the baseline of 3 is appropriate, and the optional notification_message parameter is left entirely to the schema.

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 states a specific verb and resource: sign in to Hacker News using username and password. It also names the resulting session-cookie behavior, making the tool distinct from browsing and content-action siblings, though it does not explicitly contrast with session_status.

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?

It gives clear usage context by saying the stored session cookie is for upvote, comment, and submit, which tells an agent when authenticated actions depend on this tool. It does not spell out exclusions, such as checking session_status first or avoiding redundant login calls.

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