marks

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the bar is lower, yet the description adds genuine degradation behavior: falling back to a plain legend when ImageMagick is missing, and to a fall-back-to-vision note when no tree exists. It does not cover return shape edge cases or performance costs, keeping it short of a 5.

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 purpose and the payoff (one glance replaces the zoom loop); the trailing sentences on params and fallbacks are information-dense. It is slightly long with stacked parentheticals, but each sentence carries actionable content.

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?

Given an output schema exists, the description need not detail the legend's exact return structure, and it still sketches it. Combined with sibling routing, param semantics, and both failure modes, an agent has everything needed to call `marks` correctly.

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 0%, so the description must compensate, and it does: `window` is explained as an address from desktop with focused as default, and `name` as a filter over the marked controls. Both parameters gain meaning not present in the bare schema, though format syntax for the address string is not spelled out.

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 artifact: a screenshot of a window with accessible controls drawn as numbered red marks, plus a JSON legend mapping numbers to role/name/value/click point. This is clearly distinguishable from the sibling `screenshot` (plain image) and `zoom` (magnified view) because it names the marking behavior explicitly.

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?

Explicitly routes the agent: 'read the number off the image and call `click_ui(mark=N)` (or `pointer` at the legend's x,y)', replacing the estimate-zoom-estimate loop. It also states the when-not case by naming the fallback to `screenshot` + `zoom` when the app exposes no accessibility tree.

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