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

Annotations already establish readOnly/non-destructive/closed-world, and the description goes well beyond them: it discloses the returned fields (artifact_ref, download_endpoint, download_url when storage-verified), the deliberately withheld data ('provider URLs and storage identifiers are never returned'), and the non-raising 404 shape ('{status: "not_found"}'). These are concrete behavioral traits not present in any structured field.

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?

Purpose is front-loaded and the REQUIRED/EXAMPLE lines add useful structure. The middle sentence is dense with jargon ('credential-free ArtifactDescriptor projection') but it does communicate the artifact_contract return, so little is wasted.

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?

No output schema exists, so the description carries the return-value burden and does so thoroughly (artifact_ref, download_endpoint, artifact_contract, 404 shape, withheld data). The only meaningful gap is the undocumented connection_context parameter and the absence of any auth/permission notes.

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?

With 0% schema description coverage the description must carry the param burden. It adds real value for creative_id by specifying the UUID format ('REQUIRED: creative_id (str — UUID)'), but the optional connection_context parameter and its mctx_v1_ pattern are left entirely undocumented, so only half the parameters are compensated for.

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 and resource ('Get a single creative ... by creative_id') and scopes it to resources 'owned by the authenticated tenant'. This cleanly distinguishes it from the list-style sibling creatives_list and the folder/deletion siblings, so an agent can select it without opening the schema.

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?

The description conveys what a fetch does but gives no explicit guidance on when to use this over creatives_list, creatives_list_cloud, or creatives_list_folders, and no prerequisites or exclusions. Usage is only weakly implied by 'by creative_id'.

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