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

With annotations only declaring readOnly=false, destructive=false, openWorld=true, the description carries the real behavioral weight: files are appended (not replaced), each becomes both a workspace file and a section asset, failures are reported while the rest still land, and the workspace-brand edit restriction. These are non-obvious side effects and partial-success semantics beyond what annotations state.

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 the action, then formats/limits, then naming and backdrop guidance, then the permission rule and failure behavior. Dense and largely waste-free, though the parenthetical backdrop example and repeated cross-reference make it a touch long for a 5.

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 mutating tool with no output schema, the definition covers inputs, limits, side effects, permission constraints, and partial-failure reporting. It omits the auto-create-section behavior of the kind parameter (left entirely to the schema), a minor gap for a tool of this complexity.

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 most parameters. The description still adds meaning: url is server-fetched, data is base64 for offline small files, and backdrop is explained functionally ('how pages pick the right version') rather than just as a hex pattern. The kind/auto-create-section parameter is left to the schema, keeping this at 4.

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 + resource ('Adds pictures to a brand kit section') and immediately enumerates the concrete sub-cases (logo versions, product marks, screenshots, imagery). An agent can distinguish this from sibling napkin_brand_fonts/napkin_brand_draft 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?

Gives clear operating context: which source forms are valid, size/format limits, and an explicit constraint ('you can change any kit except the workspace's brand'), cross-referenced to napkin_brand_draft for the shared rule. It does not name an explicit 'use X instead' alternative, so it falls short of a 5.

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