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

Annotations already declare idempotentHint=true, destructiveHint=false and readOnlyHint=false, so the safety profile is covered. The description adds real behavioral context beyond that: that edits apply only to a *pending* scheduled message, that cancellation is part of this tool, and that this tool is deliberately not the send path. It omits limits (e.g. the 25-item cap) and permission requirements.

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?

One dense sentence, front-loaded with the core 'what' before the sibling references. The parenthetical about scheduledMessages/id source is information-dense, though the packaging is a little thick for a single sentence.

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 no explanation, and annotations carry the safety profile. For a mutation with 0 required params, the description covers both mutation paths and the id provenance. Only minor details (item limits, partial-failure behavior) are absent.

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 only 33% (workspaceId is the documented one). The description partially compensates by mapping the two undocumented arrays to their semantics and telling the agent where the scheduled message `id` originates (get_conversations with include.scheduledMessages). It still leaves the conversationRef shape and the edit-vs-cancel field constraints to the schema, so it is additive but not fully compensating.

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+scope: 'Batch small inbox state changes' covering two concrete operations (mark read, cancel/edit a pending scheduled send). It distinguishes itself from the two overlapping siblings by name, saying concerns route to campaignstack_send_message and ids come from campaignstack_get_conversations. An agent can place it correctly without opening any schema.

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 clear when-to-use conditions ('mark conversations read, or cancel/edit a pending ... sendAt row') and explicitly names the alternative for the adjacent case: 'Sending remains campaignstack_send_message.' It stops short of stating exclusions against other edit_* tools, so it is strong context rather than a complete routing guide.

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