View the list of contacts that match a specific segment to verify targeting before sending.
Preview the contacts that match a segment without sending.
| Name | Required | Description | Default |
|---|---|---|---|
| apiKey | No | Send16 API key (overrides SEND16_API_KEY env var) | |
| segmentId | Yes | Segment ID |
Changes observed during successful MCP inspections.
v0.5.7Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries full burden. It clearly indicates no sending occurs, implying read-only behavior. However, it omits details like rate limits, required permissions, or whether the preview is real-time or cached.
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?
Single sentence, no extraneous words. Front-loaded with the action. Efficient and to the point.
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?
Simple tool with few parameters; the description covers the core function. However, the output format is not described (e.g., list of contacts, count). Completeness is high for the tool's complexity but could be slightly improved.
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 100%. The description does not add new meaning beyond the schema; it reiterates that segmentId identifies the segment. Baseline 3 is appropriate as the schema already documents both parameters adequately.
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 'Preview the contacts that match a segment without sending' clearly states the verb (preview), resource (contacts matching a segment), and subtly distinguishes from sending operations. It is specific and avoids ambiguity.
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?
The description implies usage for dry-run preview but does not explicitly state when to use this tool versus alternatives like search_contacts or preview_campaign_recipients. No when-not or alternative recommendations are provided.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.