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

Annotations already declare readOnly and openWorld, and the description adds real value beyond that: it discloses the coordinate system for returned positions and the cost model ('Free, but counts toward the scan limit'). It does not discuss failure modes or the relationship between the two image inputs, which the schema covers.

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 core action, then the output shape, then the usage link. Nothing is wasted.

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?

There is no output schema, so the description usefully explains that the result is lines of text with positions. The only gap is that with zero required parameters, it doesn't clarify that exactly one of image_url or image_base64 must be supplied, though the schema implies it.

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%, so the schema already explains image_url and image_base64 fully. The description adds no parameter-specific meaning beyond that, so the 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?

States a specific verb (read) and resource (every line of text in an image), plus the shape of the result (position 0-1000 from top left). This clearly distinguishes it from siblings like replace_text and get_edit.

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 names a use case and the sibling it feeds: 'Use it to find the exact "from" text for replace_text.' That is strong routing guidance, but it stops short of stating when not to use it or naming other alternatives.

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