WRITE: change a subscriber's contact data (email, first name, last name, phone). Only the fields you pass are sent. Ask the user to confirm the new values.
| Name | Required | Description | Default |
|---|---|---|---|
| No | New email address. | ||
| phone | No | New phone number in international format, e.g. +12025550151. | |
| last_name | No | New last name. | |
| first_name | No | New first name. | |
| subscriber_id | Yes | Recurpay subscriber id (from recurpay_list_subscribers). |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds crucial behavioral details beyond the annotations and schema: 'Only the fields you pass are sent,' which is essential for partial updates (PATCH behavior). It also includes a workflow hint: 'Ask the user to confirm the new values.' This is valuable process context.
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?
The description is front-loaded and very concise. It uses a clear structure (WRITE tag, main purpose, scope constraint, workflow advice) to provide maximum value in minimum space.
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?
The description provides a complete picture of the operation, including its partial update nature and the recommended user interaction flow, even without an 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 coverage is 100%, so the description doesn't need to redefine parameters. However, the description adds semantic meaning by specifying the required ID format: 'Only the fields you pass are sent,' implying optionality for the other fields.
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?
Uses the explicit command 'WRITE' to define its function. It clearly states the target resource ('subscriber's contact data') and the specific actions being performed (changing email, name, phone).
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 when to use it—only for updating contact data, suggesting other tools like `recurpay_get_subscriber` would be used first to find the ID. However, it doesn't explicitly state 'do not use for' or compare it to siblings like a general 'update_subscriber' call.
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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