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

Annotations are minimal, so the description carries the transparency burden. It adds useful context that this uses an existing key and can serve as a re-authentication fallback, but it does not disclose side effects such as whether existing stored credentials are replaced or whether repeated calls are harmless.

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 tightly scoped sentences, each carrying distinct information: function, preference condition, and fallback/negative instruction. No filler or repetition of schema or annotation data.

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 one-parameter authentication tool, the description covers what, when, and how, and names the relevant alternative. Output expectations are handled by the existence of an output schema, and the low complexity means nothing critical 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?

The input schema has no field descriptions, so the description must compensate. It adds meaningful detail about the single api_key parameter: it must be an existing key with the zsc_ prefix. It could go further by explaining how to obtain or pass the key, but the parameter is simple and mostly self-evident.

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 specific verb and object: 'Authenticate this connector with an existing zsc_ API key.' It also differentiates from the sibling account_signin_start by stating this tool is preferred when the key is already in the conversation.

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 a clear condition ('when the key is already in the conversation') and an explicit fallback path ('If the connector shows Connected but org tools fail, call this or account_signin_start'). The 'do not look for a Connect button' instruction prevents a common wrong action.

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