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

Annotations cover only the generic safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true); the description adds the behavior that matters: exact one-entry step semantics, the sign-in-prompt cancellation side effect, that FORM_RESUBMISSION_REQUIRED means nothing is reloaded or resubmitted, and that ORIGIN_NOT_ALLOWED leaves the tab unmoved and is recoverable. That is genuine context beyond the annotations, and nothing contradicts them.

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 core action, then the history-step rule, then edge cases and error codes. Dense but every sentence carries distinct behavioral information; the error-code list is compact. Slightly packed, but 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?

With no output schema, the description carries the return/error burden and does it well: it enumerates the meaningful failure codes and their consequences. The remaining gap is the undocumented sessionId parameter, which an agent needs in order to invoke the tool correctly.

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 only 50%: idempotencyKey is fully documented in the schema, but sessionId has no description anywhere. The description never mentions either parameter, so it does not compensate for the undocumented sessionId or explain what a session id must reference for this tool. Below the 3 baseline because of that gap.

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?

"Go back one history entry in the delegated tab" states a specific verb (go back), resource (browser history entry), and scope (the delegated tab). It explicitly contrasts with browser_forward ("back and forward move exactly one browser history entry") and browser_navigate, so an agent can distinguish it from siblings without reading schemas.

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?

It names concrete situations: after a cancelled sign-in an extra back may be needed, when a sign-in prompt is up back cancels the prompt instead of stepping history, and for form submissions it says "Use navigate instead." The alternative is named explicitly with the condition that selects it.

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