Render map changes

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

No annotations are provided, so the description carries the full burden, and it does well: it discloses return content (text summary plus PNG with yellow/green outlines), the default comparison behavior, and the edge case where no earlier version exists ('it says so'). It is silent on performance or size limits beyond the tileSize auto-reduction, but the core behavior is transparent.

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?

A single dense paragraph that front-loads what the tool produces before covering comparison options and usage guidance. Every sentence contributes, though the paragraph is long and could be broken into bullet points for faster scanning.

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 annotations and no output schema, the description fully covers the return format, the nested against object's variants, default behavior, and the no-baseline edge case. An agent has everything needed to call it correctly and interpret the result.

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?

With 67% schema coverage, the description adds real meaning: it explains the default comparison target and the semantics of against.session and against.changeset beyond the schema's terse notes. tileSize is not discussed in the description, but the schema already documents its auto-reduction behavior, so the marginal gap is small.

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: 'Show what changed on a map compared with an earlier version,' and immediately specifies the two outputs (text summary of changed tile cells and events, plus an annotated PNG). This clearly distinguishes it from siblings like render_map and render_map_image, which render a current map without a comparison baseline.

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 names a concrete usage context ('Use it after bulk painting or generation to review exactly what you touched') and explains the three ways to choose a baseline: default most-recent backup session, against.session from list_backups, or against.changeset. It does not explicitly contrast with render_map for non-diff viewing, but the routing information is otherwise strong.

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