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

Adds substantial context beyond the annotations: it does not send or start anything itself, requires an API key, and that an existing contact with the same address is OVERWRITTEN and moved onto this list. That overwrite detail substantiates the destructiveHint=true annotation with the specific data-loss mechanism rather than merely restating it.

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?

Four short paragraphs, front-loaded with the core action and consequence before prerequisites. Slightly more prose than strictly necessary, but each paragraph carries distinct information (purpose, consequence, failure/overwrite semantics, prerequisites).

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?

With no output schema, the description covers the mutation semantics an agent needs: prerequisites, failure modes, idempotency behavior, overwrite risk, and the fact that it triggers downstream outreach. Nothing material to correctly invoking a consequential bulk-add tool is missing.

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 100%, so the schema already documents listId, leadIds, and campaignId, including the 1-500 range and the default list behavior. The description largely repeats the bulk limit and adds no syntax or format detail beyond the schema, so the baseline of 3 applies.

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: 'Add saved leads to a campaign's contact list in bulk, up to 500 at a time.' It also disambiguates from related actions by clarifying that it does not send messages or start the campaign, which an agent could otherwise confuse with start_autopilot.

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 explicit context ('how leads enter an outreach sequence'), a prerequisite ('verify addresses with verify_emails first'), and a concrete failure condition (leads must belong to the authenticated account or the call fails). It routes the agent toward verify_emails and explains the consequence of ignoring that advice.

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