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

Goes well beyond the readOnly/idempotent annotations: it names the PERMISSION_REQUIRED failure mode and where the user fixes it, discloses the Pexels license and attribution duty, and warns that results follow uploader keywords rather than image content. That is exactly the kind of non-obvious operational detail annotations cannot convey.

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 and return payload, then the operational caveats. Most sentences earn their place, though the read_skill cross-reference is cryptically phrased and slightly interrupts the flow.

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?

With no output schema, the description takes on the burden of describing the return shape and does so completely: id, dimensions, duration, author, thumbnail URL, available qualities, and the downloaded flag. Combined with error behavior and the keyword-matching caveat, an agent has everything needed to call and interpret it.

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 all eight parameters are already documented in the input schema and the baseline of 3 applies. The description adds context about the output shape (dimensions, duration, thumbnail) but nothing new about parameter syntax or enum behavior for kind, size, color, or orientation.

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 first clause gives a specific verb and resource (search the Pexels stock library for photos or videos) and states the credential dependency. It is clear in isolation, but it never names its nearest siblings (search_media, download_stock_media), so an agent cannot distinguish them from the description alone.

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 rather than stated: the 'downloaded' flag hints that this feeds a download step, and read_skill {topic:'verify'} points to a follow-up, but there is no explicit when-to-use/when-not or comparison against search_media. The empty-query case is documented only in the schema, not the description.

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