name: api-field-descriptions description: | Patterns for writing clear, consistent API field descriptions including types, constraints, examples, and edge cases.

trigger: |

Writing API field documentation
Documenting request/response schemas
Creating data model documentation

skip_when: |

Writing conceptual docs → use writing-functional-docs
Full API endpoint docs → use writing-api-docs

related: complementary: [writing-api-docs]

API Field Descriptions

Field descriptions are the most-read part of API documentation. Users scan for specific fields and need clear, consistent information.

Field Description Structure

Every field description answers: What is it? (purpose), What type? (data type), Required? (mandatory), Constraints? (limits/validations), Example? (valid data)

Table Format (Preferred)

| Field | Type | Required | Description |
|-------|------|----------|-------------|
| id | uuid | — | The unique identifier of the Account |
| name | string | Yes | The display name of the Account (max 255 chars) |
| status | enum | — | Account status: `ACTIVE`, `INACTIVE`, `BLOCKED` |

Note: Use — for response-only fields (not applicable for requests).

For nested objects: status.code, status.description

Description Patterns by Type

Type	Pattern	Example
UUID	"The unique identifier of the [Entity]"	`id: uuid — The unique identifier of the Account`
String	"[Purpose] (constraints)"	`code: string — The asset code (max 10 chars, uppercase, e.g., "BRL")`
String (format)	"[Purpose] (format example)"	`email: string — Email address (e.g., "user@example.com")`
Enum	"[Purpose]: `val1`, `val2`, `val3`"	`type: enum — Asset type: \`currency`, `crypto`, `commodity``
Boolean	"If `true`, [what happens]. Default: `[value]`"	`allowSending: boolean — If \`true`, sending permitted. Default: `true``
Integer	"[Purpose] (range)"	`scale: integer — Decimal places (0-18)`
Timestamp	"Timestamp of [event] (UTC)"	`createdAt: timestamptz — Timestamp of creation (UTC)`
Object (jsonb)	"[Purpose] including [fields]"	`status: jsonb — Status information including code and description`
Array	"List of [what it contains]"	`operations: array — List of operations in the transaction`

Required vs Optional

In Requests:

Yes = Must be provided
No = Optional
Conditional = Required in specific scenarios (explain in description)

In Responses: Use — (response fields are always returned or null)

Special Field Documentation

Pattern	Format
Default values	"Results per page. Default: 10"
Nullable fields	"Soft deletion timestamp, or `null` if not deleted"
Deprecated fields	"[Deprecated] Use `route` instead"
Read-only fields	"Read-only. Generated by the system"
Relationships	"References an Asset code. Must exist in the Ledger"

Writing Good Descriptions

Don't	Do
"The name"	"The display name of the Account"
"Status info"	"Account status: `ACTIVE`, `INACTIVE`, `BLOCKED`"
"A number"	"Balance version, incremented with each transaction"
"The code"	"The asset code (max 10 chars, uppercase)"
"The timestamp"	"Timestamp of creation (UTC)"

api-field-descriptions