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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent write, so the safety profile is covered. The description adds value on top: it fixes the coordinate origin (top left) and scale (fractions of width/height), and discloses that entitySlug pins are GM-only, which is an authorization fact absent from the schema and annotations. It does not say what happens on duplicate coordinates or whether entitySlug requires a pre-existing page.

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 short sentences, front-loaded with the action, then the coordinate contract, then the entitySlug exception and return value. No filler or repetition of the tool title.

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 an 8-parameter creation tool with a fully documented schema and no output schema, the description covers the hard parts: coordinates, map/campaign targeting context, and the GM-only entity pin case. The gap is 'Returns: The pin' — with no output schema, an agent still does not know what fields a pin carries (id, body, privacy) for follow-up calls.

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 baseline is 3; the description still adds meaning by restating the coordinate frame as a single mental model ('fractions of the map's width and height, from the top left') and by explaining that entitySlug binds the pin to a page rather than merely labeling it. It leaves body/title/isPrivate entirely to the schema, which is acceptable given full coverage.

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?

Opens with a specific verb and resource ('Put a pin on a map'), and the coordinate-frame sentence makes the operation unambiguous. It does not name the sibling it is distinct from (update_pin for existing pins, list_pins/list_my_private_pins for reading), so differentiation is left partly to the name.

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 parenthetical 'A pin carrying `entitySlug` is that page's place on the map (GM only)' gives a real conditional-use rule and a permission constraint. However, there is no guidance on when to call this versus update_pin, nor any note about duplicate pins at the same spot or preconditions on the target map.

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