fetchImage

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

Beyond the readOnlyHint annotation, the description discloses that images are never OCR'd or converted, that results preserve input order and include paths plus bytes, and that a failing item is isolated while the rest still return. This is substantial behavioral context that an agent cannot infer from the schema alone.

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?

Two sentences carry the purpose, a usage example, parameter constraints, return format, partial-failure behavior, and sibling routing with no filler. The vision-oriented use case is front-loaded, and every sentence earns its place.

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 single-parameter tool with no output schema, the description fully covers accepted input types, limits, ordering, return values, error isolation, and the key alternative. An agent has everything needed to select and invoke the tool 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?

The schema already documents the sources array, its 1–50 item boundaries, and the path/order behavior. The description adds value by including a concrete invocation example and mentioning 'harvest handles' as an accepted input form not listed in the schema. This is meaningful but not essential enrichment over near-total schema coverage.

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 action and resource: fetching images as local files for vision. It includes natural-language triggers ('get this figure / photo / scanned page') and explicitly distinguishes itself from the sibling fetch by routing documents, PDFs, and web pages elsewhere.

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 exactly when to invoke fetchImage (for images to be passed to vision) and demonstrates the call shape with an explicit example. It also names the alternative tool, fetch, for non-image content, providing clear selection criteria without ambiguity.

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