store_credential

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

With no annotations, the description carries the behavioral disclosure burden. It adds critical context that credentials are stored locally and never sent to a server, which is a key behavioral trait. Nevertheless, it does not disclose behavior for duplicate site entries or overwrites, so it is not fully transparent.

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 three sentences, front-loaded with the primary purpose, and every sentence adds value: local storage claim, security guarantee, and parameter guidance. No wasted words.

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 three-parameter keychain storage tool, the description effectively covers the main context—what it saves, where it saves it, and how to identify the site. The presence of an output schema reduces the need to explain return values, but the description could still clarify behavior for existing credentials.

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 0% description coverage, so the description must compensate. It provides a clear example for the 'site' parameter ('indiehackers', 'twitter', 'gmail') and ties the parameters together as 'login credentials.' However, it leaves 'username' and 'password' entirely to their self-explanatory names, offering no additional constraints or semantics.

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 the tool's function with a specific verb and resource: 'Save login credentials to the system keychain.' It also distinguishes itself from sibling browser automation tools by specifying a local system keychain, making the purpose unambiguous.

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 provides context on when to use the tool—for securely storing credentials locally—and emphasizes that credentials are never sent to a server, which indirectly advises against use for server-side storage. However, it does not explicitly mention alternative tools or exclusions, so it falls short of a perfect score.

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