add_to_cart

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

With no annotations, the description carries the full burden of disclosing behavior. It mentions that a new cart is created if none exists ('Creates a new cart if none exists') and highlights the server-side nature and browser sync requirement. This goes beyond the bare function name and adds meaningful side-effect information. However, it doesn't mention error handling or how duplicates are treated.

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 description is concise: two sentences with the key action front-loaded. The second sentence provides essential operational context (server-side only, browser sync) without unnecessary fluff. It earns its place and remains easy to parse.

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 simple mutation tool with no output schema and no annotations, the description covers the essential aspects: what it does, side effect of cart creation, and the critical sync requirement. It doesn't detail error cases or return values, but those are less critical given the simplicity. The sibling tool list adds context that this is one of several cart operations.

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?

The tool description says 'by SKU' but does not explain the structure of the items array or the qty parameter. However, the input schema provides descriptions for both sku ('Product SKU (e.g. "T000089179")') and qty ('Quantity to add'), so the schema already carries the parameter explanation. The description adds only minimal emphasis on SKU, so it meets the baseline without substantial additional value.

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 clearly states the tool's function: 'Add products to Selver.ee guest cart by SKU.' It uses a specific verb (add), identifies the resource (Selver.ee guest cart), and specifies the method (by SKU). This distinguishes it from sibling tools like search_products, view_cart, and remove_from_cart.

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 provides explicit usage context: it is server-side only, and if a browser is open on selver.ee/cart, the agent must also dispatch cart/addItem via chrome-devtools-mcp to keep the browser in sync. This is an explicit alternative/requirement that guides when to use this tool in conjunction with other actions.

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