Sign In with Email

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

With no annotations, the description carries the full behavioral burden and largely fails: it says nothing about what a successful sign-in returns (session/token), failure modes for invalid credentials, or rate limiting. For an authentication tool this is a meaningful gap.

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?

A single front-loaded sentence with no wasted clauses. It is terse, but every word contributes and nothing is buried.

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 an auth boundary tool with no annotations and no output schema, the definition should explain the result of a successful call and the failure contract. It omits both, leaving the agent to guess what it gets back after authenticating.

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 description coverage is 100% with both required parameters (email, password) documented, so the schema does the heavy lifting and a 3 is the baseline. The description adds no syntax, format, or constraint detail beyond what the schema already states.

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 names a specific verb and resource ('signs in an existing user') plus the credential mechanism ('using email and password'), which is clearer than a bare title restatement. It partially distinguishes from horizon_signup_email via 'existing user', but does not explicitly differentiate from horizon_signin_anonymous.

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?

There is no when-to-use guidance, no prerequisites, and no mention of alternatives such as horizon_signin_anonymous or horizon_signup_email. The only implicit signal is 'existing user', which is too weak to count as direction.

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