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

Annotations already cover the safety profile (readOnly=false, destructive=false, idempotent=false, openWorld=false), so the description isn't required to restate them. It does add two things annotations cannot convey: the operation is credit-free, and it requires OAuth or an 'Authorization: Bearer acd_live_…' header, which is essential operational context for calling it at all. It stops short of explaining what the revision/concurrency behavior means for repeated calls.

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?

The purpose sentence is front-loaded and tight, and the layout modes are enumerated in one clause. The sign-in block is longer than the functional text but is necessary auth information not carried anywhere else in the definition.

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?

An output schema exists, so return values need not be described, and annotations carry the mutation safety profile. The description covers scope, cost, and auth. It omits only the concurrency implications of the revision parameter, which is a minor gap for a non-destructive layout tool.

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 80%, so the schema already documents gap, ids, revision, and canvas_id well. The description only reinforces the ids semantics ('chosen cards or the whole board') and echoes the layout values already present as an enum, adding little beyond the structured fields. Baseline 3 is appropriate.

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 description gives a specific verb ('Lay out') plus the resource ('chosen cards or the whole board') and enumerates the three output arrangements (grid, row, column), matching the layout enum. It is immediately clear what the tool does, though it never names or contrasts the adjacent siblings (move_cards, group_cards) that an agent might confuse it with.

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?

'Chosen cards (or the whole board)' implies the optional-ids case, and 'Costs no credits' is a genuinely useful decision signal. However there is no explicit when-to-use guidance or any statement of when to prefer this over move_cards or group_cards, so usage must be inferred.

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