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

Annotations already declare readOnlyHint=true, and the description does not contradict that. It adds real behavioral context beyond the annotations: a 1024px maximum scale, the fact that the image is the bare map with no query overlay, and the X/Z orientation across the heatmap bounds. It does not cover return format, error behavior for a missing or not-yet-uploaded background image, or caching, which keeps it at a solid 3.

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?

Front-loaded with the core action, then the use case, then the key caveat, then the coordinate convention and prerequisite — every sentence adds a distinct piece of information with no repetition or 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?

With no output schema, the description does the work of describing the returned image (bare top-down map, max 1024px, X horizontal / Z vertical) and includes the required skill prerequisite, which is good. It still omits what happens when a heatmap has no uploaded background image and whether the response is a URL or binary payload, leaving a gap for an agent handling edge cases.

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% and each parameter already documents its source (list_heatmaps, list_projects), so the schema carries the burden. The description mentions the heatmap's bounds, which loosely relates to heatmapId but adds no syntax, format, or constraint detail beyond what the schema provides. Baseline 3 is appropriate.

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 ("Fetch a heatmap's background image") and immediately narrows it with concrete identifying detail: the top-down map of the game region uploaded by the SDK, capped at 1024px. This separates it cleanly from data-returning siblings like run_heatmap_query.

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 states the use case explicitly — see layout and name places when explaining heatmap query hotspots — and rules out a misreading by noting query results are not drawn on the map. It also gives an ordering prerequisite (load the heatmap-queries skill first) but never names the sibling tool an agent should call instead when it actually wants hotspot data.

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