File Generation — Reference

Skills can generate files (PDF, DOCX, CSV, images, etc.) during execution. Generated files are automatically stored and made available for download.

How It Works

When a skill runs, Heym creates an _output_files/ directory in the skill's execution environment. The path is available as the _OUTPUT_DIR environment variable.

Any file written to this directory (except files starting with _) is captured after the skill completes, stored in the file system, and a download link is generated automatically.

Writing Files in a Skill

import os
import json
import sys
import csv
 
args = json.load(sys.stdin)
output_dir = os.environ.get("_OUTPUT_DIR", ".")
 
# Generate a CSV
csv_path = os.path.join(output_dir, "report.csv")
with open(csv_path, "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["Name", "Value"])
    writer.writerow(["Revenue", args.get("revenue", 0)])
    writer.writerow(["Users", args.get("users", 0)])
 
print(json.dumps({"status": "Report generated"}))

PDF Generation

The reportlab library is available for PDF generation:

import os
import json
import sys
from reportlab.lib.pagesizes import A4
from reportlab.pdfgen import canvas
 
args = json.load(sys.stdin)
output_dir = os.environ.get("_OUTPUT_DIR", ".")
 
pdf_path = os.path.join(output_dir, "invoice.pdf")
c = canvas.Canvas(pdf_path, pagesize=A4)
c.drawString(100, 750, f"Invoice for {args.get('customer', 'Unknown')}")
c.drawString(100, 730, f"Amount: ${args.get('amount', 0)}")
c.save()
 
print(json.dumps({"status": "Invoice generated"}))

DOCX Generation

The python-docx library is available:

import os
import json
import sys
from docx import Document
 
args = json.load(sys.stdin)
output_dir = os.environ.get("_OUTPUT_DIR", ".")
 
doc = Document()
doc.add_heading(args.get("title", "Report"), level=1)
doc.add_paragraph(args.get("content", ""))
doc.save(os.path.join(output_dir, "report.docx"))
 
print(json.dumps({"status": "Document generated"}))

Multiple Files

Skills can generate multiple files in a single execution:

import os
import json
import sys
import csv
 
args = json.load(sys.stdin)
output_dir = os.environ.get("_OUTPUT_DIR", ".")
 
# Generate CSV
with open(os.path.join(output_dir, "data.csv"), "w") as f:
    writer = csv.writer(f)
    writer.writerow(["col1", "col2"])
    writer.writerow(["val1", "val2"])
 
# Generate text summary
with open(os.path.join(output_dir, "summary.txt"), "w") as f:
    f.write("Summary of the data processing...")
 
print(json.dumps({"status": "done", "files_generated": 2}))

File Size Limits

Generated files are subject to the FILE_MAX_SIZE_MB configuration (default: 99 MB). Files exceeding this limit are silently skipped.

Download Links

After execution, each generated file gets a unique download URL. These URLs are included in the skill's output under the _generated_files key:

{
  "_generated_files": [
    {
      "id": "550e8400-e29b-41d4-a716-446655440000",
      "filename": "report.csv",
      "mime_type": "text/csv",
      "size_bytes": 1234,
      "download_url": "https://your-domain.com/api/files/dl/abc123..."
    }
  ]
}

The id field is the file UUID. Use it with the Drive node to manage the file from within the workflow — delete it, add a password, set an expiry, or limit downloads:

$agentLabel._generated_files[0].id

These links can also be shared directly or managed through the Drive tab.

Depending on deployment configuration, download_url can be either:

An absolute URL (when FRONTEND_URL is configured for the backend container).
A relative path (for example /api/files/dl/abc123...), which still works in the browser UI.

Supported MIME Types

File types are automatically detected from the file extension. Common types:

Extension	MIME Type
.pdf	application/pdf
.docx	application/vnd.openxmlformats-officedocument.wordprocessingml.document
.csv	text/csv
.json	application/json
.txt	text/plain
.png	image/png
.jpg	image/jpeg

Drive Node - Programmatic delete, password, TTL, download limits, and team share/unshare on generated files
Drive - Dashboard Drive tab and share-link behavior
Drive Tab - Browse and manage files in the UI