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

Goes well beyond the annotations by naming the three failure modes (HTTP_AUTH_REQUIRED, NO_HISTORY_ENTRY, ORIGIN_NOT_ALLOWED), stating whether the tab moves, and flagging ORIGIN_NOT_ALLOWED as recoverable. That is real behavioral context, though the interaction with the idempotencyKey replay window is left to the schema.

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 core action is front-loaded in the first sentence and the remainder is dense, non-redundant edge-case and error documentation. It is longer than average but nearly every clause adds a distinct rule an agent would otherwise have to discover by trial.

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 two-parameter navigation tool with no output schema, the description covers success semantics, all failure codes, whether the tab moves, and the recovery path. An agent has enough to call it and to interpret any result without further documentation.

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 50%: idempotencyKey is thoroughly documented in the schema, but sessionId has no description and the description does not explain it either, only implying via "delegated tab" that state is session-scoped. Baseline 3 fits for a tool whose schema carries most parameter meaning.

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: "Go forward one history entry in the delegated tab." The follow-up sentence explicitly contrasts it with back, letting an agent separate it from the sibling browser_back without reading either 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?

Covers the normal case (one history entry), the sign-in-cancel edge case where an extra back is needed, and the blocked case with concrete alternatives: "Call back (cancels the prompt) or navigate elsewhere." That is explicit when-to-use and when-to-do-something-else guidance.

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