Set a cookie

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

Annotations only flag readOnlyHint=false, so the description earns credit for disclosing upsert semantics ('create or replace'), scoping rules, and host-only behavior. It does not say what happens to a pre-existing cookie's other attributes (secure/httpOnly/sameSite) when replaced, which is the remaining behavioral gap.

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?

Two tight sentences: the action and upsert semantics come first, then scoping guidance, then a verification pointer. Nothing redundant with the schema is restated.

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 an 8-parameter mutation with no output schema, the description covers upsert behavior, scoping, and how to confirm the result. It would be complete if it resolved the required-vs-optional domain question and noted that non-specified attributes are defaulted rather than preserved on replace.

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 the baseline is 3. The description adds real meaning about domain/path scoping, but it also says 'omit domain for a host-only cookie' while the schema marks domain as required — a conflict that leaves the agent unsure whether the call will succeed without it.

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 ('Create or replace one cookie') and names the underlying primitive (BiDi storage.setCookie), which cleanly separates it from browser_get_cookies, browser_delete_cookies, and the various import_cookies siblings.

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 concrete usage context: domain/path scope the cookie, omit domain for host-only, and verify afterwards with browser_get_cookies. It does not explicitly contrast with browser_delete_cookies or the import_cookies tools, but the intended use case is unambiguous.

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