Create multiple contacts at once in bulk. Do not include sensitive personal data (health, financial, government ID, payment card, passwords).
| Name | Required | Description | Default |
|---|---|---|---|
| dry_run | No | Validate and show what would be created without creating anything | |
| list_id | Yes | List ID for all contacts | |
| contacts | Yes | Array of contact objects |
Changes observed during successful MCP inspections.
Input schema / properties / contacts / descriptionPrevious value: -"Array of contact objects,required"New value: +"Array of contact objects"Input schema / properties / contacts / items / properties / custom_fields / descriptionPrevious value: -"Custom field values. Only keys returned by list_custom_fields. Values: text, number, or date (YYYY-MM-DD). Do not include sensitive personal data (health, financial, government ID, payment card, passwords)."New value: +"Custom field values, keyed by the field ID, name or key shown by list_custom_fields. Values: text, number, or date (YYYY-MM-DD). Do not include sensitive personal data (health, financial, government ID, payment card, passwords)."Input schema / properties / contacts / items / properties / email / descriptionPrevious value: -"Contact email address,required"New value: +"Contact email address"Input schema / properties / list_id / descriptionPrevious value: -"List ID for all contacts,required"New value: +"List ID for all contacts"Input schema / properties / api_keyRemoved value: -{
- "description": "MailerCloud API key",
- "type": "string"
-}Input schema / properties / dry_runAdded value: +{
+ "description": "Validate and show what would be created without creating anything",
+ "type": "boolean"
+}Input schema / properties / contacts / items / properties / city / descriptionAdded value: +"City"Input schema / properties / contacts / items / properties / company_name / descriptionAdded value: +"Company name"Input schema / properties / contacts / items / properties / contact_typeRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / country / descriptionAdded value: +"Country"Input schema / properties / contacts / items / properties / custom_fields / descriptionAdded value: +"Custom field values. Only keys returned by list_custom_fields. Values: text, number, or date (YYYY-MM-DD). Do not include sensitive personal data (health, financial, government ID, payment card, passwords)."Input schema / properties / contacts / items / properties / department / descriptionAdded value: +"Department"Input schema / properties / contacts / items / properties / email / descriptionAdded value: +"Contact email address,required"Input schema / properties / contacts / items / properties / first_name / descriptionAdded value: +"First name"Input schema / properties / contacts / items / properties / idRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / industryRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / job_title / descriptionAdded value: +"Job title"Input schema / properties / contacts / items / properties / last_name / descriptionAdded value: +"Last name"Input schema / properties / contacts / items / properties / lead_sourceRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / list_idRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / middle_nameRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / phone / descriptionAdded value: +"Phone number"Input schema / properties / contacts / items / properties / postal_codeRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / salaryRemoved value: -{
- "type": "string"
-}Input schema / properties / contacts / items / properties / state / descriptionAdded value: +"State"Input schema / properties / contacts / items / properties / tags / descriptionAdded value: +"Tags to assign"Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare non-readOnly, non-idempotent, non-destructive, open-world behavior, so the safety profile is covered. The description adds genuinely useful compliance context (sensitive data prohibition) but says nothing about partial-failure handling, what happens to contacts that already exist, or batch size limits — significant gaps for a bulk write.
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 scope. The second sentence earns its place as a compliance constraint, though it partially duplicates the same warning embedded in the custom_fields schema description.
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?
For a bulk mutation with no output schema, an agent still lacks information about how per-contact results or errors are returned and whether the operation is atomic. Annotations cover the mutation safety profile, but the batch-specific behavior an agent needs is not described.
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%, including per-field descriptions inside the nested contact object, so the schema carries parameter meaning. The description adds only that contacts are handled in bulk and repeats the sensitive-data restriction already present in the custom_fields schema text.
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 with explicit bulk scope ('Create multiple contacts at once in bulk'), which implicitly separates it from the single-record create_contact sibling. It does not name the alternative tools outright, so the differentiation is inferred rather than stated.
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 the bulk wording, and there is an explicit must-not rule about sensitive personal data. However, there is no guidance on when to prefer this over create_contact or upsert_contact, nor any mention of the dry_run option for pre-validating a batch.
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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