update-contactModify an existing contact's email, name, unsubscribe status, or custom fields by ID or email address.
Update an existing contact. Can be identified by ID (con_xxx) or email address.
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | The contact ID (con_xxx) or email address. | |
| No | New email address. | ||
| last_name | No | New last name. | |
| first_name | No | New first name. | |
| unsubscribed | No | Global unsubscribe status. | |
| custom_fields | No | Replace custom fields. |
Changes observed during successful MCP inspections.
v2.0.3Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations at all, the description carries the full behavioral burden and does not meet it: it says nothing about required permissions, whether the operation is reversible, how unmentioned fields are treated, or what the response contains. Only the identifier acceptance rule is conveyed.
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 followed by the single non-obvious calling convention. No filler.
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 six-parameter mutation tool with a nested object and no annotations or output schema, the description is too thin — partial-update semantics, custom_fields replacement consequences, and response behavior are all left unaddressed.
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 schema already documents every parameter including the ID-or-email convention. The description restates that convention but adds no new semantics (e.g., custom_fields replacement behavior lives only in the schema). 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 ('Update an existing contact') and adds the identifier convention (con_xxx or email). It does not differentiate itself from siblings like create-contact or get-contact, but the intent is unambiguous.
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?
No guidance on when to use this versus create-contact/get-contact, no prerequisites, and no statement of whether unspecified fields are left untouched or cleared. An agent must infer partial-update semantics on its own.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.