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

The annotations already declare the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=true), so the bar is lower, yet the description still contributes real behavioral context: the trial grows to 10 addresses and the user receives a passwordless WozApi account with e-mail-code login. It does not mention idempotency or the 10-address cap being a hard limit.

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?

Three short sentences, front-loaded with the core action, followed by consequences and the key guardrail. No filler or repetition; every sentence carries information.

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?

With no output schema, the description usefully explains the outcome of the call (account creation, login mechanism, address count). It is sufficient for correct invocation, though it omits what happens when the address is already present or the trial is full.

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%, so both parameters are already fully documented. The description only restates the email constraint ('only an address the user typed'), adding no syntax or format detail beyond the schema baseline.

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 opens with a precise verb+resource: adds an e-mail address to an existing trial. It does not, however, explicitly distinguish itself from the sibling start_trial or explain the relationship between starting a trial and adding addresses to it, so an agent must infer the boundary.

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 one clear constraint ('Only use an address the user typed'), which is genuine usage guidance, but says nothing about when to call this versus start_trial or other sibling tools, nor any prerequisites beyond what the schema already states for trial_code.

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