tabs_groups_update

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

With no annotations, the description carries the full burden and does well: "Leaves the group's tabs where they are" discloses partial-update semantics (membership untouched), and the version requirement and at-least-one-field rule are behavioral facts the schema cannot express. It omits error/failure behavior and whether the change is reversible, keeping it below a 5.

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 mutation and its scope land in the first sentence, followed by the non-obvious semantic ('leaves the group's tabs where they are') before the boilerplate prerequisites. Every sentence carries information an agent needs; nothing is repeated from the schema.

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?

Output schema exists, so return values need not be explained, and the description covers the mutation scope, the at-least-one-field rule, the Firefox prerequisite and profile scoping. The remaining gap is what happens on an invalid or stale group_id, which an agent calling a mutation would benefit from knowing.

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 baseline is 3; the description earns above that by stating the cross-parameter constraint that at least one of title/color/collapsed must be supplied, which the schema (all nullable, default null) does not enforce. It also ties profile_id to profiles_list and warns that object IDs are profile-local and non-transferable, adding meaning beyond the bare integer type.

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?

"Change a tab group's title, colour or collapsed state" is a specific verb and resource with the mutable fields enumerated, so an agent knows exactly what is being altered. It does not explicitly name the sibling it differs from (tabs_group creates, tabs_groups_query reads), so it stops short of full sibling differentiation.

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?

"Give at least one of title, color or collapsed" states the precondition for a meaningful call, and "Requires Firefox 139+" plus "obtain it from profiles_list" give the agent prerequisites and the sourcing path for profile_id. It does not rule out alternatives or state what to do when the group does not exist, so no exclusion guidance.

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