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

Annotations already declare readOnly=false, destructive=false and openWorld=true, so the mutation profile is known. The description adds genuinely non-obvious behavior beyond that: leads already in the campaign, unsubscribed, bounced, suppressed or with invalid addresses are silently skipped rather than erroring, which tells the agent the call is partial-success tolerant. It omits any note on limits or what the response reports back.

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?

Two short sentences, front-loaded with the action and followed by the skip conditions. No filler or repetition of the title.

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?

The skip rules are a valuable addition, but for a mutation tool with an undocumented required 'id' parameter, an unmentioned allLeads flag and no output schema, the description leaves real gaps. An agent could not confidently determine what to pass as 'id' or how the bulk mode behaves from this text alone.

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 25% (just allLeads), so the description carries most of the burden. It explains leadIds/listIds conceptually but never clarifies that the required 'id' is the campaign identifier (that field has no schema description), and it never mentions allLeads at all, leaving a whole input mode undocumented in prose.

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 and resource ('Add leads ... to a campaign') and distinguishes itself from create_campaign/import_leads by naming the target campaign operation. It is clear what the tool accomplishes, though it never explains how it differs from the related import_leads sibling.

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?

Usage is implied by 'from lists (or by id)', which hints that either listIds or leadIds can drive the call, but there is no explicit when-to-use guidance versus import_leads or the bulk allLeads path. Nothing tells the agent which of the three input modes to prefer.

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