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

Annotations already indicate a mutating, non-idempotent operation. The description goes beyond that by clarifying that it creates a secure session, returns its id, and has no UI. It does not detail session lifetime or side effects, but for an internal helper this is meaningful added context.

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?

One concise sentence front-loads the purpose, then immediately adds the usage caveat and redirects to the correct sibling. Every clause contributes information without repetition or filler.

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 internal helper with two optional, well-documented parameters dollar, the description states what it creates, what it returns, and that agents should use a different tool. The lack of an output schema is mitigated because the return value is specified as the session id.

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 schema fully describes both optional parameters (carrier and language) with 100% coverage. The description adds no additional parameter-level detail, so the baseline of 3 applies.

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: it creates a secure session and returns its id. It also explicitly marks itself as an internal helper and distinguishes itself from start_eligibility_check, so an agent can tell it apart from sibling 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 an explicit exclusion: 'No UI; agents should use start_eligibility_check instead.' This clearly tells agents not to use this tool and names the correct alternative, leaving no ambiguity about when it should be invoked.

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