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

With no annotations, the description carries the full burden, and it does disclose the key behavioral traits: the write overwrites the field's current value, submit triggers Enter, and credential input is blocked with a defined fallback path. It does not cover wait/timing, error behavior, or rate limits, but the mutation and security semantics are clearly surfaced.

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?

Front-loaded with the purpose, then the critical exclusion, then a compact per-parameter list. Every sentence earns its place and there is no padding, though the trailing parameter glossary is slightly terse rather than elegantly integrated.

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?

An output schema exists, so return values need not be explained. Purpose, exclusions, fallback routing, and all three parameters are covered, leaving only operational edge cases (page-load waits, failure modes) unaddressed, which is acceptable for this tool class.

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 0%, so the description must compensate, and it documents all three parameters: selector with a concrete CSS example ('input[name=url]'), text as the value to type, and submit as 'press Enter afterwards'. The example selector syntax is genuinely additive beyond the bare schema types, though 'text: what to type' is thin.

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 target ('Type into a form field') and immediately qualifies scope with '(replaces its value)'. It also names a sibling (fill_secret) that must be used instead for credentials, so an agent can distinguish it without opening any schema.

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?

Gives an explicit when-not ('Never use this for the owner's passwords or codes') plus the correct alternative branching in both cases: fill_secret when the sign-in is saved, otherwise request a takeover. This is exactly the when/when-not/alternative guidance called for.

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