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

Annotations cover read-only, idempotent, open-world, and non-destructive behavior. The description adds valuable behavioral detail: it returns an inline image, requires exact case-preserved slugs, and crucially states 'An unavailable preview is not an invented image' to prevent hallucination.

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?

Front-loaded with purpose, then workflow guidance, slug format, and failure behavior. Every sentence earns its place, though the second sentence is somewhat long and agent-instructional.

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 preview tool with full schema coverage and rich annotations, the description covers purpose, return format (inline image), slug requirements, and failure behavior. It is nearly complete, though it doesn't specify image dimensions or error response format.

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. The description adds meaning beyond the schema by specifying that slug is 'exact, case-preserved' and that it can be a 'Poly Haven slug or Sketchfab uid', which clarifies format and source mapping.

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 (preview), resource (asset's thumbnail), output format (inline image), and timing (before importing). This clearly distinguishes it from sibling tools like assets_search, asset_import, and asset_generate_3d.

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 says to use it before importing and for candidate suggestions with source/license, offering reuse/adapt/build. It does not name explicit alternatives or when-not-to-use cases, but the context is clear enough for an agent.

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