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

Beyond the annotations, the description reveals significant non-obvious behavior: the call is atomic, any invalid run rejects the entire operation, and the set remains unchanged on failure. It also states the required permission scope (comparisons:write), which the agent cannot infer from the schema.

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 two sentences with every clause contributing: operation, ownership/status precondition, atomicity, rollback guarantee, and permission. The primary action is front-loaded and the exception behavior follows compactly without filler.

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 two-required-param mutation with no output schema, the description is complete: it covers the action, preconditions, failure semantics, rollback behavior, and authentication scope. There are no hidden edge cases that would prevent a correct invocation.

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?

With 0% schema description coverage, the description must supply parameter meaning, and it does: session_ids are the runs to append, and set_id is the target set. It also attaches value constraints (finished, owned, not already a member) to those parameters. The only gap is that it never explicitly names set_id or session_ids.

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 uses a specific verb and resource: 'Append finished runs you own to a set.' It clearly differentiates this operation from set-creation and set-inspection sibling tools. The all-or-nothing detail reinforces that this is a mutation of an existing comparison set.

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?

It clearly identifies the intended use case: adding already-finished, owned runs to a set, and lists the reasons a call would be refused. It does not explicitly name alternative tools such as create_comparison_set, but the context is unambiguous enough to route an agent correctly.

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