Ajv

The Fastify target writes its own Ajv validators from your contract when you link none. Ajv checks the request as JSON Schema, and the server names each issue by the contract rule.

Used by: Fastify only, when its entry has no validators link.

Set up

Nothing to add: leave out the validators entry and the validators link, and install ajv in your app. The Fastify target writes the validators in its own validators/ folder.

npm install fastify ajv @seampact/server-runtime @seampact/hooks

To use zod or yup instead, add a validators entry and link it (Switch the validator).

What you get

The files have the same layout as the zod ones. Each schema is a JSON Schema handed to Ajv through an adapter. For the CreateTask schema of the overview, trimmed from validators/schemas/input.ts:

export const CreateTaskSchema = ajvStandardSchema({
  type: "object",
  properties: {
    title: {
      type: "string",
      minLength: 1,
      maxLength: 200,
      seampactMessages: {
        minLength: "Expected at least 1 character.",
        maxLength: "Expected at most 200 characters.",
      },
    },
    effort: { type: "integer", minimum: 0, maximum: 9007199254740991 },
  },
  required: ["title"],
  additionalProperties: false,
});

additionalProperties: false refuses a key the contract does not declare. seampactMessages carries the text of each failure. One Ajv validator checks the whole request, and the reply lists every issue.

When a check fails

Each Ajv error becomes one issue of the 400 body. The adapter names it by the contract rule, such as minLength or required, never by Ajv’s keyword.

Native or consistent rules

The Fastify target has no rules option.

Limits

The generator refuses by name a oneOf, a property default and the other forms in Generate fails.

Next

• Fastify.
• The 400 body: When a check fails.