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

Goes well past the destructive/openWorld/non-idempotent annotations: it discloses async background execution with multi-minute latency, the thrown-error preconditions with literal messages, and the non-obvious side effect that a child campaign is created (which explains why campaign_delete reports removing active children). This is exactly the context structured fields cannot carry.

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?

Front-loaded with the core action, then preconditions, then alternatives, then the child-campaign note. Dense but each sentence carries real information; the campaign_delete cross-reference is slightly tangential but justifies itself as a side-effect disclosure.

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 compensates by stating it runs in the background and can take minutes, so the agent knows not to expect immediate leads. It doesn't say what is returned or how to track progress of the background job, which is the one remaining gap for an async mutation.

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% and each property (url, type, field, query, campaignId) is documented in the schema, so baseline 3 applies. The description adds only an implicit mapping of 'new source' to the `type` enum and does not clarify which of url/field/query applies to which type branch.

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: 'Top up an already-running campaign with prospects from a new source, without touching its sequence or existing leads.' This is immediately distinguishable from campaign_create, campaign_set_source, and campaign_upload_leads 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?

Explicitly names the when-not case ('this is never how a new campaign gets its audience') and routes to the two correct alternatives by name, campaign_set_source and campaign_upload_leads. Two hard preconditions (ACTIVE, first batch filtered) are stated with the exact backend error string.

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