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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered; the description adds two things beyond them — that results are only the briefs the signed-in user can reach (permission scoping) and that the payload is short summaries rather than full records. It stops short of describing pagination behavior or what a summary contains.

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?

Three tight sentences, front-loaded with what is listed and what is returned, then the sibling redirect, then the narrowing options. No filler.

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 read-only list tool with four safety annotations, full schema coverage, and no output schema, the description covers purpose, output granularity (summaries), scope, and narrowing. Only default page size / result-volume expectations are left implicit.

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 six parameters are already documented in the schema at a baseline 3. The description reinforces only two of them (project and script-by-name narrowing) and says nothing about search, page, per_page, or how project vs project_id interact.

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 ("List the thumbnail briefs") plus the access scope ("the signed-in user can reach"), and explicitly contrasts the result with the full-record sibling get-thumbnail-brief. An agent can tell it apart from create-thumbnail-brief/update-thumbnail-brief/get-thumbnail-brief without opening any 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?

"call get-thumbnail-brief for one in full" gives a clear alternative-and-condition, and the last sentence explains when to narrow by project or script name. What is missing is a note on when not to use it (e.g., the general `search` sibling for cross-entity lookup).

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