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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, and the word "Appends" is consistent with an additive, non-destructive write. Beyond that, the description adds no auth/permission requirements, no note on what happens to existing slides, and no error/limit behavior, so it adds only modest behavioral context.

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 tight sentences, front-loaded with the action, then the layout/content rules, then the prerequisite. The inline enumeration of all eleven layout keys duplicates the schema's layout description verbatim, which is a minor waste of space.

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 5-param additive write with no output schema, the description covers the required inputs (layout, boardId implied by "existing deck"), optional title/content, and a pre-flight check. It omits what the call returns (e.g., the new slide id) and the workspace-token nuance, which lives only in the schema.

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 100%, so the baseline is 3, but the description genuinely adds meaning: how `content` maps onto each layout, the `---` block splitting, and that two-column/comparison take one block per column. That is semantics the schema's terse "Markdown body — blocks split on `---` lines" does not convey.

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?

"Appends one slide to an existing deck" gives a specific verb (appends) and resource (slide within a deck), which is distinct from the sibling mutators napkin_slide_update and napkin_slide_fill. The behavior is clear, though it never names those siblings to explicitly disambiguate add-vs-fill-vs-update.

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 provides one concrete workflow step — "Check the deck first with `napkin_deck_outline`" — but gives no guidance on when to use this versus napkin_slide_fill, napkin_slide_update, or napkin_deck_write/compose. Usage is implied rather than stated with alternatives or exclusions.

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