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

No annotations are supplied, so the description carries the burden; it does disclose a real side effect (the outgoing focused document is persisted into the session's document map) plus the return content. However, it states unconditionally that the call 'returns the now-focused document's HTML', which conflicts with include_html defaulting to false (token-light ids/title/section count only). Auth requirements are also unaddressed.

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?

Three compact sentences with the core action stated first and the id semantics and side effect following. The parenthetical asides are dense but each carries information; nothing is padding.

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 mutation tool with no annotations and no output schema, the description does cover the state change and the return channel. It still leaves the HTML-vs-token-light return behavior ambiguous despite include_html existing, and says nothing about required authorization, so an agent could easily expect a payload it will not receive by default.

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 description adds genuinely useful semantics for document_id — that either a session slot id or a durable_document_id UUID is valid — which the bare 'Document Id' schema title does not convey. But with only 25% schema coverage it leaves session_id and authorization unexplained, and its unconditional 'returns ... HTML' claim overrides rather than supports include_html's documented default of false.

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?

Names a specific verb+resource ('Make document_id the focused document') and immediately defines what 'focused' means in operational terms: the editor's active document and the default edit target. It is clearly separable from siblings such as open_documents, close_session_document, and list_session_documents.

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?

Explains which identifier forms are accepted and where to obtain them (the session slot id, or the permanent UUID surfaced by list_documents/Files and returned as `durable_document_id` by list_session_documents). This is concrete routing guidance, but it never states when to prefer this over open_documents or close_session_document, so no true alternatives/exclusions are given.

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