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

With no annotations provided, the description carries the full burden of behavioral disclosure. It transparently states that the tool only switches between already-open documents, that it errors on ambiguous names, and that it does not load from disk. This covers error conditions and scope, which is exactly the kind of behavioral context an agent needs. No important behavior is left undisclosed.

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 description is three sentences with zero wasted words. The core purpose is front-loaded in the first clause, and every subsequent sentence adds necessary guidance: parameter selection, error handling, and the contrast with open_document. It is tightly structured and efficiently informative.

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?

Given that the tool has only two optional parameters, no output schema, and no annotations, the description covers all the essential information an agent needs: what it does, how to provide arguments, when to use index instead of name, and when not to use it (in favor of open_document). Nothing critical is missing for a correct invocation.

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?

The input schema already describes both parameters at 100% coverage, so the baseline is 3. The description adds extra semantic value by stating that the two parameters are mutually exclusive ('Pass exactly one of the two'), that index is 0-based and sourced from list_documents, and that name should be avoided when ambiguous. These details go beyond the schema definitions and help the agent choose the correct parameter in context.

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?

The description opens with a specific verb and resource: 'Switch focus to an already-open document,' which clearly states the tool's action and target. It also distinguishes itself from the sibling tool open_document by explicitly noting that only documents already open are affected, and that open_document is for loading from disk. This mapping leaves no ambiguity about what the tool does.

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?

The description provides explicit usage instructions: 'Pass exactly one of the two,' clarifies the mutual exclusivity of the name and index parameters, and explains when to prefer index over name for disambiguation. It also gives a direct contrast with open_document, telling the agent exactly when not to use this tool. This is comprehensive and leaves little to inference.

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