read_image

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

With no annotations, the description carries the full burden, but it only states the basic operation (fetch and return bytes) without disclosing error handling, failure modes, authentication needs, or rate limits. The extensive post-fetch instructions about describing the image are about downstream analysis, not the tool's own behavior.

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?

The description is bloated with a long block of instructions on how to describe the image after retrieval, which is tangential to the tool's core purpose. While the first two sentences are concise, the additional field list makes the description unnecessarily long and less scannable.

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 simple fetch operation, the description adequately explains the main function and the schema covers parameters. However, it lacks details about return format (beyond 'bytes'), possible errors, and does not clarify whether the post-fetch image description guidance is required or optional. It is moderately complete but not thorough for a tool with no output schema.

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 input schema already provides complete descriptions for both parameters (url and max_size_mb), so baseline 3 applies. The description adds minimal extra meaning by reiterating 'image URL' but doesn't explain URL format or size-limit behavior beyond the schema.

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 clearly states the verb and resource: 'Fetch an image URL and return its bytes for vision analysis.' It also references a specific sibling tool ('scan_unique_images') to contextualize its use, which helps distinguish it from alternatives.

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 provides explicit context by saying 'Pair with scan_unique_images to inspect images already on the site,' which implies a workflow. However, it does not offer exclusions or compare against other sibling tools like read_images, so it's not fully explicit about when not to use.

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