keychain_store_credential

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

With no annotations, the description carries the full burden of explaining side effects, but it does not mention overwrite behavior, return values, errors, or whether the stored credential is immediately available to the browser. It only states that it stores securely.

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?

The description is a single concise sentence that includes the action, resource, and purpose. No unnecessary words or details are present.

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 store operation, the description gives the essential purpose, but it omits behavioral details such as whether existing credentials are overwritten or what the tool returns. Given the lack of annotations and output schema, this is a moderate gap.

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 already provides clear descriptions for all three parameters with 100% coverage. The description does not add extra meaning beyond what is already in the schema, so the baseline score of 3 is appropriate.

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 clearly states a specific action (store), a specific resource (macOS Keychain), and the intended purpose (so the browser agent can log in automatically later). It distinguishes the tool from siblings like browser_autofill_login and passkey_save_registration.

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 implies when to use the tool (before an automated login), but it does not explicitly mention alternatives or conditions for not using it. The purpose is strong enough that an agent can infer the primary use case.

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