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

Annotations already declare non-read-only, non-destructive, non-idempotent, so the safety bar is lower. The description still adds real value by stating the additive semantics — existing content is preserved and new content goes at the end — which is the key differentiator from a full rewrite. It does not warn that repeated calls will duplicate content or what happens if documentId is unknown.

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 the mutation and its scope front-loaded, followed by required inputs and a concrete use case. 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?

For a two-parameter write tool with full schema coverage and safety annotations, this covers what an agent needs to select and call it. The only gap is return behavior — no output schema and no statement of what comes back or whether the appended content is echoed.

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 100%, with both parameters documented including the 200k maxLength, so the baseline is 3. The description only restates the required parameter names, adding no format or syntax detail beyond the schema.

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 ('Append markdown to the END of an existing Library document') and pins the scope with 'END' plus 'keeping its current content'. This cleanly distinguishes it from siblings like update_document, create_document, and get_document.

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?

Gives a concrete usage trigger: adding a section such as action items or a dated entry 'without rewriting the whole doc'. That implicitly routes the agent away from update_document, but it never names the alternative explicitly or states when not to use this tool.

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