JSON Schema Manual

What it is: a draft 2020-12 schema over a field list someone already confirmed - validating structure, never inventing business rules.

Overview

Produces JSON Schema from a confirmed canonical field list, for validation, API contracts, import and export structures, form generation, and schema documentation.

JSON Schema validates structure. It does not compute, decide or imply. This is a helper: it defines no table of its own and renders whatever field list the active module already confirmed, so the property names here are the names that module uses in its CSV, SQL, spreadsheet and Notion mapping.

Layer: n/a. Fits: every stage. Table code: n/a - it renders the active module's table.

When to Use This Skill

• I need a JSON Schema
• validate this payload before it goes in
• make an API contract for this table
• document the shape of this import file
• generate a form from this schema
• turn the agreed fields into a schema

Also use it when a module has confirmed a field list and the user wants the contract for the system that will read it, rather than the table itself.

Do not use it to add validation the business has not asked for. A schema is a promise about what a payload may contain, and every restriction in it rejects real data.

How It Works

Follow the shared execution contract. The module-specific rules below define only domain fields, decisions, calculations, and safety constraints.

Step 1 - Identify intent

Read the request and pick the intent before asking anything.

• "I need a schema" -> a strict or permissive schema, per Step 5.
• "something rejected my payload" -> review or fix: only the rule that caused it.
• "which fields are required" -> advice: answer from the confirmed field list, and offer the schema rather than emitting one.

Build only what was requested. A fix does not become a rewrite, and advice does not become a file.

Step 2 - Ask only what is missing

Reuse everything already confirmed, including by the module that owns the field list: the property names and types, the select options, the date and currency fields, the calculated fields, the statuses and the IDs. Never ask again for information the user has already supplied.

Ask one short question per message, and only when the answer changes the schema:

Q: Should the schema reject unknown fields, or allow them?

Nothing else is worth a question. Requiredness, options and formats come from the confirmed field list, not from a new round of asking.

Step 3 - Hold the internal context

Hold the answers in this shape. It stays internal - it is not shown to the user unless they ask, and it never carries a value the user did not give.

module: json-schema-manual
intent: null            # set in Step 1, one of: schema, review, fix, advice
source_module: null     # the module whose field list this renders
draft: "https://json-schema.org/draft/2020-12/schema"
additional_properties: null   # false | true - asked once, then held
example_instances: false
confirmed_facts: []     # only what the user actually said
open_questions: []      # the unanswered ones, in the order worth asking

source_module is the one field this skill needs that a module skill does not have. If it is unknown, ask which table the contract is for, because a schema built from a guess rejects the real data.

Step 4 - Recommend the smallest workflow

Build an already requested artifact without asking again. For advice-only requests, give a short recommendation and offer the relevant artifact.

Recommended approach: one object schema, one property per confirmed field, no required entry the field list does not mark as required, and no enum the field list does not define. Strictness only where the contract is closed.

Why this one: a schema's damage is asymmetric. A property it omits passes data nobody reviewed; a property it marks required, or an enum it invents, rejects data that was perfectly valid. Confirm the closed rules and stay silent on the rest.

Workflow: Field list confirmed -> Properties typed -> Requiredness applied from the source -> (validated) -> Published as the contract

Step 5 - Build only on request

Once the user asks, emit the schema as data only. Keep prose outside machine-readable data; provide file links and material limitations separately. Property names come from the confirmed field list, identical to the CSV, SQL, spreadsheet and Notion names, in the same order. Never rename a property independently.

Default draft:

https://json-schema.org/draft/2020-12/schema

Type mapping

Canonical type	JSON Schema
id	integer or string, matching the confirmed source
title	string
text	string
long_text	string
number	number
currency	number
percentage	number
date	string, format: date
datetime	string, format: date-time
checkbox	boolean
select	string
multi_select	array of string
url	string, format: uri
email	string, format: email
phone	string
relation	string or integer, matching the confirmed reference key
files	array or string, only when the source structure defines it

Required

A property goes in required only when the parent skill marks it required, or the user explicitly confirms it. Unknown requiredness means optional, and requiredness is never inferred from what a business obviously needs - a calculated value is never required when its source may legitimately be missing.

Select options

enum only for confirmed options:

{
  "Status": {
    "type": "string",
    "enum": ["Draft", "Filed", "Paid"]
  }
}

Never invent an enum value. Where options are a starting set rather than a confirmed taxonomy, leave the property a plain string and say the options are not yet fixed.

Additional properties

"additionalProperties": false only when the contract is meant to be strict:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "...",
  "type": "object",
  "properties": {},
  "required": []
}

If strictness is unknown and it matters, ask the one question in Step 2. Otherwise follow the parent skill's convention.

Null handling

Do not add null to a type automatically. Allow it only where the parent schema explicitly distinguishes null from missing. For unknown or optional data, prefer omission over invented null semantics - a validator that accepts null where the data model has no such value is a rule nobody agreed to.

Examples and descriptions

No examples, no instance data, and no description beyond what the source field definition supports. Examples only when the user asks for them, and then obviously fake. A description that invents meaning becomes the spec, and the spec then rejects real data.

Calculated fields

A calculated output field is represented by its data type and nothing else. The schema does not carry the calculation, and a consumer that reads the field gets the value the producing system computed - never one this schema invents.

Before you hand it over

Property names exactly match the canonical fields?
Types aligned with the source?
Every `required` entry supported by the source?
Every `enum` confirmed?
No invented formats?
No fake examples?
No schema drift against the other artifacts?

Field Reference

This skill has no Field Reference of its own, and it must not grow one. The active module's Field Reference is the single source: its property names here, its CSV columns, its SQL columns and its Notion properties are the same field list, so a payload that validates is a payload the module can read.

If the field list is not in front of you, read skills/<slug>/SKILL.md for the module in play. If it is missing or ambiguous, ask which table the contract is for and stop.

See the Input Modules reference for the full guidance.

Select Options

enum values are the confirmed taxonomy, never a starting set presented as final. Where the business has not settled its options, the property stays a string and the mapping notes that the options are open - a schema is a contract, and an unconfirmed list becomes a rejection waiting for a real record.

Relations

A relation is a reference key: string or integer, matching whatever the source uses as the key. The schema does not describe the target table, does not check that the target exists, and cannot express the link as a reference. Do not add a property for the target's fields; that is a second schema, and the user has not asked for one.

Examples

Prompt

Give me a JSON Schema for the invoices table so our API can validate a payload.

Answered in one message, no intake needed - the field list was already confirmed:

Read skills/invoices-billing/SKILL.md for the field list, then emit the draft 2020-12
object schema with those properties in that order, `required` carrying only the fields the
module marks required, and `additionalProperties: false` only if the payload is closed.

Prompt

The API rejected a payload because Amount was a string.

Fix only - one rule, no rewrite:

Amount is number in the schema, so "1250.50" fails. Send it unquoted. The same applies to every numeric field, and dates stay ISO strings in format: date.

Documented shape - a strict schema over a confirmed field list. The properties below are a documentation example: emit the real field list, not this one.

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Invoice Register",
  "type": "object",
  "additionalProperties": false,
  "properties": {
      "Invoice ID": { "type": "string" },
      "Client": { "type": "string" },
      "Invoice Date": { "type": "string", "format": "date" },
      "Total": { "type": "number" },
      "Status": { "type": "string", "enum": ["Draft", "Sent", "Paid", "Overdue"] }
  },
  "required": ["Client", "Total", "Status"]
}

See the Best Practices reference for the full guidance.

Limitations

• It validates structure. It does not check a value against a database, confirm that a client exists, or compute anything.
• A schema is only as good as the field list behind it, and it cannot repair a list that was never confirmed.
• Formats such as date and email are annotations: many validators treat them as advisory, so a payload that validates may still be wrong.
• No versioning, no publication, no registry, and no CI wiring. That is the consuming system's job.
• Cross-field rules - a due date after an invoice date, a total equal to a sum - are not expressible here and are not checked.
• Nothing is verified until the user validates a real payload against it.

See the Security & Safety Notes reference for the full guidance.