Add a single contact. Adding a contact records consent to email them — only add addresses that opted in, or the send will damage sender reputation and may breach CAN-SPAM/GDPR.
| Name | Required | Description | Default |
|---|---|---|---|
| tags | No | Segmentation tags | |
| Yes | Contact email address | ||
| source | No | Where this contact came from (max 100 chars) | |
| last_name | No | Last name (max 100 chars) | |
| first_name | No | First name (max 100 chars) | |
| custom_fields | No | Custom key-value attributes |
Changes observed during successful MCP inspections.
Input schema / properties / companyRemoved value: -{
- "description": "Company name (max 150 chars)",
- "type": "string"
-}Input schema / properties / job_titleRemoved value: -{
- "description": "Job title (max 100 chars)",
- "type": "string"
-}Input schema / properties / phoneRemoved value: -{
- "description": "Phone number (max 50 chars)",
- "type": "string"
-}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare a non-read-only, non-idempotent write. The description goes beyond them by disclosing a meaningful side effect: that adding a contact records consent to email, with reputational and CAN-SPAM/GDPR consequences. This is real behavioral context not encoded in the annotations.
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 tightly written sentences with zero waste. The core action is front-loaded and the compliance caution follows immediately without padding.
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 full schema coverage and annotations covering the safety profile, the description supplies the one thing structured fields cannot: the consent/compliance semantics of the operation. It does not address duplicate handling or behavior when the email already exists, which is a minor gap given no output schema.
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%, so all six parameters (email, tags, source, names, custom_fields) are already documented in the schema. The description adds no syntax, format, or uniqueness detail beyond that, so baseline 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 and resource: 'Add a single contact.' The word 'single' implicitly separates it from the bulk import_contacts sibling, but no sibling is named, so the differentiation is left to inference rather than made explicit.
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?
Provides a genuine when-not condition ('only add addresses that opted in'), which is real selection guidance and a stronger condition than typical. However, it never names alternatives such as import_contacts for bulk adds or update_contact for existing records, so the routing is incomplete.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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