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

Annotations cover the read-only/idempotent/open-world profile, but the description adds real behavioral context the annotations cannot: per-type return rendering (images as viewable images, text as text, PDFs as embedded files depending on client) and a hard 10 MB size limit. That is genuine value beyond structured fields.

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?

Four short sentences, front-loaded with the action and examples, then the return behavior and the size cap. No filler; the multi-sentence structure is justified by the different return types.

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-param fetch tool with no output schema, the description covers accepted inputs, return modality per file type, and the 10 MB limit. Only minor gaps remain (what happens on oversized/failing fetches, pagination not applicable).

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 0% for the single 'url' param, so the description must carry the meaning, and it does via concrete accepted URL formats ([image: ...], piazza.com upload links). It stops short of format/encoding details, but the examples are useful compensation for the coverage gap.

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+resource ('Open a file or image that a post links to') and gives concrete examples of acceptable URL shapes. No sibling does this, so it is clearly distinguished from the listing/reading tools in the sibling set.

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?

Usage is implied by the examples (an [image: ...] link or a piazza.com upload link) but the description never says explicitly when to use this vs. reading a post directly, nor any preconditions. Adequate but not routing-level guidance.

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