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

Annotations only declare readOnly=false, openWorld=false, destructive=false; the description adds the meaningful state precondition (drafts/paused only) plus content-format rules (plain text blank-line paragraphs, simple HTML, template/spintax syntax, mandatory {{unsubscribe}} in the first email). That is real behavioral context beyond the structured fields, though it says nothing about what happens to the prior sequence or about validation failures.

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 replacement semantics are front-loaded, followed by the nested-shape rules and then the templating vocabulary; each clause adds information no other field supplies. The templating sentence is dense but still readable, and there is no padding.

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-parameter but deeply nested write tool with no output schema, the description covers structure and templating well but omits the meaning of `id`, the timing fields (waitDays, sameThread), variant weighting/activation, and confirmation of what happens to the previously stored sequence. It is adequate to attempt a call but not to call it confidently in edge cases.

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 description coverage is 0%, so the description carries the documentation burden, and it does explain the shape of `steps`: ordered, 1–5 variants each, body as text or HTML. However it never explains `id`, nor the per-step `waitDays`/`sameThread` or per-variant `subject`/`active`/`weight`, leaving several parameters undocumented in both schema and description.

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 opens with a concrete verb+resource ('Replace the whole sequence') and the title reinforces it, so an agent immediately knows this is a full overwrite rather than an incremental edit. It does not name the sibling write_sequence, which is the natural alternative for non-replacement edits, so sibling differentiation is only implied by the word 'whole'.

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 gives an explicit eligibility condition ('Only drafts and paused campaigns'), which tells the agent when the call will succeed versus fail. It stops short of naming write_sequence as the alternative for already-launched campaigns, so the routing guidance is incomplete but still actionable.

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