Add one phone number to a party record with a single request. Prevents overwriting existing numbers by targeting only the new entry.
Append a single phone number to a party. Atomic — one PUT to Capsule. Use this instead of update_party.phoneNumbers for single-entry adds.
| Name | Required | Description | Default |
|---|---|---|---|
| type | No | Free-form label, e.g. 'Work', 'Mobile'. | |
| number | Yes | ||
| partyId | Yes |
Changes observed during successful MCP inspections.
v2.3.0Input schema / requiredPrevious value: -[
- "number"
-]New value: +[
+ "partyId",
+ "number"
+]v1.7.0v1.6.2v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotations already indicate this is a non-read-only, non-destructive operation. The description adds useful behavioral context by stating the operation is atomic and performs a single PUT to Capsule, and by framing it as an append rather than an update. It does not cover error handling or duplicate behavior, but the added atomicity context goes beyond 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 tight sentences with no filler. The core action is front-loaded, and the routing guidance is stated immediately after the behavior. Every word earns its place.
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 simple three-parameter operation with no nested objects or enums, the description covers the action, atomicity, and the key alternative. It does not describe return values, but there is no output schema and the operation is simple enough that this omission is not critical. A minor gap is the lack of any prerequisite note, such as the party needing to exist.
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 only 33%, so the description should compensate. It clarifies that 'number' is a phone number and that the operation appends a single entry, but it does not explain partyId or type beyond what the parameter names and the existing schema description for type already provide. The parameter meanings are recoverable, but the description adds limited per-parameter value.
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 states a specific verb and resource: 'Append a single phone number to a party.' It also differentiates itself from update_party.phoneNumbers, making the tool's distinct purpose immediately clear. The sibling tools include add_party_email_address and remove_party_phone_number_by_id, so this precise action is well separated.
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?
'Use this instead of update_party.phoneNumbers for single-entry adds' explicitly names the alternative and the condition under which this tool should be chosen. This gives an agent clear routing guidance without needing to inspect update_party's schema.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.