cred_fill

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

With no annotations, the description carries the full burden and does so well: it discloses that the password is decrypted and injected by a local credential proxy, never surfaces in return values or model context, and that origin must match the binding saved at record time. It does not describe success/failure outcomes or the submit side effects in detail.

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 dense sentences, front-loaded with the core action, followed by the security behavior and the origin constraint. Every sentence adds distinct value with no 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 7-parameter mutation tool with no annotations and no output schema, the description supplies the critical behavioral and safety context. It partially compensates for the missing output schema by noting the password is absent from returns, but leaves success/failure behavior and the optional-submit side effect to the schema.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning: it clarifies the security semantics of the password flow and the origin-match requirement that the schema only illustrates with an example URL. The handle/origin lookup precedence remains in the schema.

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?

States a specific verb and resource ('把已保存的账号密码填进当前页面并可选提交') and clearly establishes scope as saved credentials rather than arbitrary values. It is distinguishable from browser_fill_form and cred_list, though it never names those siblings explicitly.

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?

Usage is implied by the action ('fill saved credentials, optionally submit') and by the origin-binding constraint, but there is no explicit when-to-use / when-not-to-use guidance and no routing to cred_list or browser_fill_form. Adequate minimum but with a clear gap.

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