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

Annotations already flag destructiveHint=true; the description adds the non-obvious mechanics: section-level replacement rather than merging, regenerated step/variant ids, and atomic rejection ("the whole call is then rejected and nothing changes"). This is exactly the behavior an agent could not infer from the schema. Minor tension worth noting: the annotation claims idempotentHint=true while the text says ids are regenerated on each replacement, though the resulting data state is equivalent.

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?

Three sentences, front-loaded with the patch semantics, and each clause carries information. The second sentence is long and semicolon-heavy, requiring a careful read to parse the replacement rule and the id-regeneration consequence.

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 deeply nested mutation schema with no output schema, the description covers the critical semantics: partial update scope, replacement granularity, and the blocking precondition. It does not mention permissions/ownership requirements or what is returned after a successful update, which leaves a small gap given the tool's 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 baseline is 3, but the description adds real meaning by explaining the replace-vs-patch contract for `sequence` and the `settings` sub-objects, which the schema does not state. It does not describe the required `id` or the inheritance behavior of mailboxes/tracking beyond the schema's own note.

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 subsequence" gives a clear verb plus resource, and the opening word "Change" plus the PATCH-style explanation makes it distinguishable from create_subsequence and update_campaign. It does not explicitly name sibling tools for routing, so it stops just short of a 5.

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 states the operating context: only supplied fields change, but each settings section and `sequence` are full replacements. It also gives an explicit when-not — emails of a running subsequence cannot be replaced — without naming an alternative tool, so it is clear context rather than full alternative routing.

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