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

Annotations cover the safety profile (readOnly=false, idempotent=false, openWorld=true) but say nothing about side effects. The description adds real behavioral context: new emails are silently signed up and issued an api_key (an account-creating side effect), the rate-limit benefit, and how to transmit the resulting session key as an Authorization: Bearer header.

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?

Four short sentences, front-loaded with the benefit and the primary api_key path before the longer OTP path. Every sentence carries information an agent needs to invoke the tool correctly.

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 describe the return value, and it does: a session key, plus the header format for using it. Combined with both auth flows and the side-effect disclosure, nothing needed for correct invocation 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%, so baseline is 3, but the description goes further by explaining the dependency between email and otp (the two-step OTP flow) and the distinct role of api_key as a shortcut path, none of which the per-field schema text conveys.

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 resource ("Sign in to b59.link") plus the concrete outcome (rate limit 2 -> 300 req/min, ownership of creations). It is unmistakably distinct from the sibling URL/QR tools, which none of them authenticate.

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 describes two invocation paths and the condition selecting each: pass api_key for an immediate session key, or pass email then call again with email+otp. The only gap is that no "when not to call" case or alternative route is stated, and the motivating condition (hitting the 2 req/min limit) is only implied.

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