apify-generate-output-schema – Coding skill for AI agents

When to Use

• Use when this upstream workflow matches the user's stated goal.
• Use when the task requires the procedures documented in this skill.

Generate Actor output schema

You are generating output schema files for an Apify Actor. The output schema tells Apify Console how to display run results. You will analyze the Actor's source code, create dataset_schema.json, output_schema.json, and key_value_store_schema.json (if the Actor uses key-value store), and update actor.json.

Core principles

• Analyze code first: Read the Actor's source to understand what data it actually pushes to the dataset — never guess
• Derive nullability from evidence: Missing, null and guaranteed fields differ; preserve actual type/runtime contracts and verify Apify validator support.
• Anonymize examples: Never use real user IDs, usernames, or personal data in examples
• Verify against code: If TypeScript types exist, cross-check the schema against both the type definition AND the code that produces the values
• Reuse existing patterns: Before generating schemas, check if other Actors in the same repository already have output schemas — match their structure, naming conventions, description style, and formatting
• Don't reinvent the wheel: Reuse existing type definitions, interfaces, and utilities from the codebase instead of creating duplicate definitions

---

Phase 1: Discover Actor structure

Goal: Locate the Actor and understand its output

Initial request: $ARGUMENTS

Actions:

1. Create todo list with all phases

2. Find the .actor/ directory containing actor.json

3. Read actor.json to understand the Actor's configuration

4. Check if dataset_schema.json, output_schema.json, and key_value_store_schema.json already exist

5. Search for existing schemas in the repository: Look for other .actor/ directories or schema files (e.g., /dataset_schema.json, /output_schema.json, **/key_value_store_schema.json) to learn the repo's conventions — match their description style, field naming, example formatting, and overall structure

6. Find all places where data is pushed to the dataset:

• JavaScript/TypeScript: Search for Actor.pushData(, dataset.pushData(, Dataset.pushData(
• Python: Search for Actor.push_data(, dataset.push_data(, Dataset.push_data(

7. Find all places where data is stored in the key-value store:

• JavaScript/TypeScript: Search for Actor.setValue(, keyValueStore.setValue(, KeyValueStore.setValue(
• Python: Search for Actor.set_value(, key_value_store.set_value(, KeyValueStore.set_value(

8. Find output type definitions — reuse them directly instead of recreating from scratch:

• TypeScript: Look for output type interfaces/types (e.g., in src/types/, src/types/output.ts). If an interface or type already defines the output shape, derive the schema fields from it — do not create a parallel definition
• Python: Look for TypedDict, dataclass, or Pydantic model definitions. Use the existing field names, types, and docstrings as the source of truth

9. Check for existing shared schema utilities or helper functions in the codebase that handle schema generation or validation — reuse them rather than creating new logic

10. If inline storages.dataset or storages.keyValueStore config exists in actor.json, note it for migration

Present findings to user: list all discovered dataset output fields, key-value store keys, their types, and where they come from.

---

Phase 2: Generate dataset_schema.json

Goal: Create a complete dataset schema with field definitions and display views

File structure

{
    "actorSpecification": 1,
    "fields": {
        "$schema": "http://json-schema.org/draft-07/schema#",
        "type": "object",
        "properties": {
            // ALL output fields here — every field the Actor can produce,
            // not just the ones shown in the overview view
        },
        "required": [],
        "additionalProperties": true
    },
    "views": {
        "overview": {
            "title": "Overview",
            "description": "Most important fields at a glance",
            "transformation": {
                "fields": [
                    // 8-12 most important field names
                ]
            },
            "display": {
                "component": "table",
                "properties": {
                    // Display config for each overview field
                }
            }
        }
    }
}

Consistency with existing schemas

If existing output schemas were found in the repository during Phase 1 (step 5), follow their conventions:

• Match the description writing style (sentence case vs. lowercase, period vs. no period, etc.)
• Match the field naming convention (camelCase vs. snake_case) — this must also match the actual keys produced by the Actor code
• Match the example value style (e.g., date formats, URL patterns, placeholder names)
• Match the view structure (number of fields in overview, display format choices)
• Match the JSON formatting (indentation, property ordering, spacing) — all schemas in the same repository must use identical formatting, including standalone Actors

When the Actor code already has well-defined TypeScript interfaces or Python type classes, derive fields directly from those types rather than re-analyzing pushData/push_data calls from scratch. Types guide inference, but verify serialized output and all runtime branches; annotations may be stale.

Generation conventions (verify against the selected Actor contract)

| Rule | Detail |

|------|--------|

| All fields in properties | The fields.properties object must contain every field the Actor can output, not just the fields shown in the overview view. The views section selects a subset for display — the properties section must be the complete superset |

| Nullability | Represent actual nullability; do not weaken guaranteed fields automatically |

| additionalProperties | Choose from the actual extensibility contract; permissiveness is not always correct |

| required | Derived from actual guaranteed fields; optional and nullable are separate |

| Anonymized examples | No real user IDs, usernames, or content |

| "type" required with "nullable" | AJV rejects nullable without a type on the same field |

> Warning — most common mistakes:

> 1. Only including fields that appear in the overview view. The fields.properties must list ALL output fields, even if they are not in the views section.

> 2. Only adding "required": [] and "additionalProperties": true on nested object-type properties but forgetting them on the top-level fields object. Both levels need them.

> Note: nullable is an Apify-specific extension to JSON Schema draft-07. It is intentional and correct.

Field type patterns

String field:

"title": {
    "type": "string",
    "description": "Title of the scraped item",
    "nullable": true,
    "example": "Example Item Title"
}

Number field:

"viewCount": {
    "type": "number",
    "description": "Number of views",
    "nullable": true,
    "example": 15000
}

Boolean field:

"isVerified": {
    "type": "boolean",
    "description": "Whether the account is verified",
    "nullable": true,
    "example": true
}

Array field:

"hashtags": {
    "type": "array",
    "description": "Hashtags associated with the item",
    "items": { "type": "string" },
    "nullable": true,
    "example": ["#example", "#demo"]
}

Nested object field:

"authorInfo": {
    "type": "object",
    "description": "Information about the author",
    "properties": {
        "name": { "type": "string", "nullable": true },
        "url": { "type": "string", "nullable": true }
    },
    "required": [],
    "additionalProperties": true,
    "nullable": true,
    "example": { "name": "Example Author", "url": "https://example.com/author" }
}

Enum field:

"contentType": {
    "type": "string",
    "description": "Type of content",
    "enum": ["article", "video", "image"],
    "nullable": true,
    "example": "article"
}

Union type (e.g., TypeScript ObjectType | string):

"metadata": {
    "type": ["object", "string"],
    "description": "Structured metadata object, or error string if unavailable",
    "nullable": true,
    "example": { "key": "value" }
}

Anonymized example values

Use realistic but generic values. Follow platform ID format conventions:

| Field type | Example approach |

|---|---|

| IDs | Match platform format and length (e.g., 11 chars for YouTube video IDs) |

| Usernames | "exampleuser", "sampleuser123" |

| Display names | "Example Channel", "Sample Author" |

| URLs | Use platform's standard URL format with fake IDs |

| Dates | "2025-01-15T12:00:00.000Z"

… (full content is in the download package)