get-numberGet information about a specific fax number.
Side effects: none (read-only).
| Name | Required | Description | Default |
|---|---|---|---|
| number | Yes | Fax number in E.164 form, e.g. +1234567890. | |
| user_id | No | Fax.Plus user ID. Default: self. |
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | ||
| number | Yes | ||
| status | Yes | ||
| owner_id | Yes | ||
| assigned_to | Yes | ||
| is_canceled | No | ||
| acquired_date | Yes | ||
| friendly_name | No | ||
| notifications | No | ||
| expiration_date | No |
Changes observed during successful MCP inspections.
Output schema / properties / friendly_nameAdded value: +{
+ "type": [
+ "null",
+ "string"
+ ]
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world behavior, and the description's 'Side effects: none (read-only)' merely restates them without adding context. Nothing is said about error behavior for unknown numbers, permissions, or what fields the lookup returns.
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, front-loaded lines with no filler. The second line is redundant with the annotations, which keeps it from a 5.
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?
Output schema exists, parameters are fully documented, and annotations cover safety, so the minimum an agent needs is present. However, for a lookup tool among many siblings (list-numbers, get-user, get-fax), the description gives no hint of what is returned or when this lookup is the right entry point.
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% — both 'number' (E.164 format with example) and 'user_id' (default: self) are documented in the schema. The description adds no parameter detail, 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 ('Get information') and resource ('a specific fax number'), which distinguishes it from list-numbers (listing) and update-number (mutation). It does not explicitly name those siblings, but the singular-resource framing makes the intent clear.
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 only implied by the resource name; there is no explicit when-to-use or when-to-prefer-list-numbers/update-number guidance. An agent can infer the read-lookup scenario but must do the routing itself.
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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