firefox_fill

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

Annotations already declare destructiveHint=true, readOnlyHint=false and idempotentHint=false, so the write/overwrite nature is structured data. The description does add real value by saying input is dispatched as 'framework-compatible input events', implying framework state is updated rather than just the DOM value. However it never states that an existing field value is overwritten (the destructive behavior) or that the snapshotId must be current.

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?

Two tight sentences with no filler, leading with what the tool does and following with the exclusion. Slightly cryptic phrasing ('their separate flows') costs a little clarity but nothing is wasted.

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?

There is no output schema, and the description does not say what a successful fill returns, whether the value replaces or appends to existing content, or what happens on a stale snapshotId. For a destructive browser mutation with 40% schema coverage, those are meaningful omissions.

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 description coverage is only 40%: only 'ref' and 'snapshotId' are documented, while 'tabId', 'value' and 'frameId' have no description anywhere. The tool description mentions no parameters at all, so it does not compensate for the three undocumented ones or clarify value length limits or frame scoping.

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?

Uses a specific verb ('Fill') and resource ('ordinary text field or editable region'), and distinguishes the scope from password, payment, auth-code and file inputs. It stops short of naming which sibling tool handles those excluded cases, so the routing is implied rather than explicit.

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?

Explicitly excludes the cases where this tool must not be used (passwords, payment fields, authentication codes, files) and points to 'their separate flows'. The only gap is that it never names those alternative tools, so an agent must still guess which sibling to call.

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