How many rows can one job have?

Up to 1,000 items per batch. Split a longer list into several jobs; there is no limit on how many jobs you run, and each counts once against the rate limit. See async and batch.

What happens when one row is wrong?

When the template fails on a row’s data, that item fails and the others still render: the job ends as partially_failed and the failed item carries the error, so you can fix the row and render it again on its own. An item the API refuses outright (a request field it does not accept, or data that misses the template’s schema under validate_data) refuses the whole batch before anything is queued, and the problem names the item’s position.

Does a failed item cost units?

No. Only documents that were produced are counted.

Can I send a spreadsheet instead of writing code?

Yes: the app takes a CSV or Excel file, maps the columns to the template’s fields and runs the batch for you. The code here is for the same thing inside your own system.

Guide · Ruby

Generate PDFs from a CSV in Ruby

A list of people and a template make a stack of documents. Instead of one request per row, a batch queues up to 1,000 renders as one job, and one zip comes back. This Ruby program reads a CSV, maps the rows and waits for the job.

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What you need

An API key. Create one in the app under API keys and export it as FORMFEED_API_KEY. A test key (ff_test_…) is right for trying things out. See the quick start.
Ruby. You need Ruby 3; the program uses net/http and json from the standard library.
The template. certificate from the certificate example, whose fields are exactly the columns of the CSV.
The CSV. attendees.csv next to the program, with a header row. It is shown below.
Enough units. Batches are part of every plan, and each item counts as at least one unit. On the Free plan a live batch is refused when the month has fewer units left than the batch has items; a test key is not counted. The limits page has the units per plan.

The program

The program reads the CSV, turns every row into an item, queues them as one job with zip: true, waits until the job is done and saves the archive.

batch.rbRuby

require "csv"
require "json"
require "net/http"

BASE = URI("https://api-eu.formfeed.dev/v1/")

def api(method, path, body = nil)
  uri = URI.join(BASE, path)
  request = (method == :post ? Net::HTTP::Post : Net::HTTP::Get).new(uri)
  request["Authorization"] = "Bearer #{ENV.fetch("FORMFEED_API_KEY")}"
  request["Content-Type"] = "application/json"
  request.body = JSON.generate(body) if body
  response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: uri.scheme == "https") { |http| http.request(request) }
  answer = JSON.parse(response.body)
  abort "#{answer["title"]}: #{answer["detail"]}" unless response.is_a?(Net::HTTPSuccess)
  answer
end

items = CSV.read("attendees.csv", headers: true).map do |row|
  # every field of a CSV is text: the template expects hours as a number
  { data: row.to_h.merge("hours" => row["hours"].to_i) }
end

job = api(:post, "renders/batch", { template: "certificate", zip: true, items: items })
puts "#{job["id"]} #{job["total"]} queued"

# the job is always asynchronous: ask for it until it is no longer queued or processing
while %w[queued processing].include?(job["status"])
  sleep 2
  job = api(:get, "jobs/#{job["id"]}")
end
puts "#{job["succeeded"]}/#{job["total"]} rendered, #{job["failed"]} failed"

File.binwrite("certificates.zip", Net::HTTP.get(URI(job["zip_url"]))) if job["zip_url"]

Run it

It prints the job id and how many renders were queued, then 4/4 rendered, 0 failed, and certificates.zip lies next to the program with one PDF per row, 0001-document.pdf to 0004-document.pdf.

Shell

export FORMFEED_API_KEY=ff_test_...
ruby batch.rb

What is particular about Ruby

Hashes become JSON. Symbol keys are fine: JSON.generate writes them as strings, and the API’s snake_case names are idiomatic Ruby anyway.
abort with the problem. A problem document carries a title and a detail; the program prints both and exits with status 1.
In Rails. Put the call in a job (Active Job, Sidekiq), not in the request cycle: a synchronous render answers when the PDF is done, which can take up to 60 seconds before the API answers 202 and finishes in the background.

The CSV

One header row, one line per document. The columns are the fields the template expects, so no mapping table is needed:

attendees.csvText

name,course,completed_on,hours
Erika Mustermann,Analytical Engines 101,2026-09-10,16
Max Mustermann,Analytical Engines 101,2026-09-10,16
Jane Doe,Print CSS for developers,2026-09-11,8
John Doe,Print CSS for developers,2026-09-11,8

What a batch does differently

Always asynchronous. The answer comes back at once with the status queued. The renders run in the background, as many at a time as your plan allows.
One template, many items. A top-level template applies to every item that does not name its own, so an item is usually just its data.
Partly failed is a state. A job in which some items failed ends as partially_failed (failed when all did). succeeded and failed count them, and every item is a render of its own in items, with its own error.
The zip is optional. Every item keeps its own download URL in items, which is what you want when the documents go to different people. zip: true adds one archive of the succeeded ones, each named 0001- and its item’s filename (document.pdf without one), in row order.
Or a webhook. Instead of waiting, give the batch a webhook_url and let job.completed (or job.failed, when every item failed) tell you. For thousands of documents that is the better shape: no process waiting for minutes.

When the API says no

One shape for every error. Errors are problem documents (RFC 9457) with type, title, status, detail, a stable code and the request_id to quote to support; the type URL leads to a page about that error. The list is in the error reference.
The usual ones. 401 unauthorized for a missing or revoked key, 404 template_not_found for a wrong template name, 422 template_runtime_error when the template fails on the data, 429 rate_limited above the plan’s requests per second, 402 quota_exceeded when the Free plan’s units are used up (a paid plan bills extra units up to its hard cap).
Retry safely. Send an Idempotency-Key header with the POST, and repeat the request with the same key when you do not know whether the first attempt arrived: for 24 hours the key returns the first answer instead of rendering and billing again. The answer is stored once the first attempt has been answered, so do not retry while it may still run; and problems below 500 are stored too, so a corrected request needs a new key.

The job around this program

This guide is one program. What the job needs around it, from the template to the limits and the price, is on the page Certificate generator API.

More Ruby guides

FAQ

How many rows can one job have?: Up to 1,000 items per batch. Split a longer list into several jobs; there is no limit on how many jobs you run, and each counts once against the rate limit. See async and batch.
What happens when one row is wrong?: When the template fails on a row’s data, that item fails and the others still render: the job ends as partially_failed and the failed item carries the error, so you can fix the row and render it again on its own. An item the API refuses outright (a request field it does not accept, or data that misses the template’s schema under validate_data) refuses the whole batch before anything is queued, and the problem names the item’s position.
Does a failed item cost units?: No. Only documents that were produced are counted.
Can I send a spreadsheet instead of writing code?: Yes: the app takes a CSV or Excel file, maps the columns to the template’s fields and runs the batch for you. The code here is for the same thing inside your own system.