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

Annotations already cover readOnly/idempotent/non-destructive; the description adds real value beyond them with a cost disclosure ('Costs 5¢ per call'), the vision-AI processing model, and the precondition that image_key must come from a prior read_datasheet response. It does not describe the response shape, though idempotency is confirmed by annotations.

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?

Dense and front-loaded with cost and core action before the routing guidance and example. Every sentence carries information, though the example and the parenthetical field explanations make it slightly longer than strictly necessary.

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 a read-only, idempotent vision tool with no output schema, the definition covers purpose, cost, precondition, and selection guidance against its main sibling. What it does not state is the shape of the returned answer, which is the only material gap.

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, but the description adds genuine meaning: image_key is described as 'the storage path in the image URL' sourced from read_datasheet, and question is framed as optional with an inline call example. This goes beyond the schema's terse field docs.

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 (reads with vision AI) and resource (datasheet image: graph, package drawing, pin diagram, schematic), and explicitly ties it to read_datasheet output. An agent can distinguish it from read_datasheet without opening either schema.

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: 'For exact electrical values prefer read_datasheet's text tables; use this for what only the picture shows (package dimensions, pin assignments, curve trends, approximate values off a curve).' Both the when and the when-not, plus the named alternative, are stated.

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