Documentation

Ship Excel export without owning a spreadsheet library.

POST JSON, get a styled .xlsx back. Ten rows or ten million. This page is the whole API. There is not much of it, which is the point.

Quickstart

Create a key in the dashboard, then:

curl -X POST https://api.jarrah.sh/v1/workbooks \
  -H "Authorization: Bearer $JARRAH_KEY" \
  -H "Content-Type: application/json" \
  -d '{"sheets":[{"name":"Sales",
        "columns":[{"header":"Item"},{"header":"Amount"}],
        "rows":[["Widget",1250.5],["Gadget",99]]}]}' \
  -o sales.xlsx

import requests

r = requests.post(
    "https://api.jarrah.sh/v1/workbooks",
    headers={"Authorization": f"Bearer {key}"},
    json={"sheets": [{
        "name": "Sales",
        "columns": [{"header": "Item"}, {"header": "Amount"}],
        "rows": [[o.name, o.amount] for o in orders],
    }]},
)
r.raise_for_status()
open("sales.xlsx", "wb").write(r.content)

const res = await fetch("https://api.jarrah.sh/v1/workbooks", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${key}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    sheets: [{
      name: "Sales",
      columns: [{ header: "Item" }, { header: "Amount" }],
      rows: orders.map((o) => [o.name, o.amount]),
    }],
  }),
});

if (!res.ok) throw new Error(await res.text());
await writeFile("sales.xlsx", Buffer.from(await res.arrayBuffer()));

body, _ := json.Marshal(map[string]any{
    "sheets": []any{map[string]any{
        "name":    "Sales",
        "columns": []any{map[string]string{"header": "Item"}},
        "rows":    rows,
    }},
})

req, _ := http.NewRequest("POST", "https://api.jarrah.sh/v1/workbooks", bytes.NewReader(body))
req.Header.Set("Authorization", "Bearer "+key)
req.Header.Set("Content-Type", "application/json")

res, err := http.DefaultClient.Do(req)
// res.Body is the .xlsx

res = Net::HTTP.post(
  URI("https://api.jarrah.sh/v1/workbooks"),
  {sheets: [{name: "Sales", rows: rows}]}.to_json,
  "Authorization" => "Bearer #{key}",
  "Content-Type" => "application/json",
)
File.binwrite("sales.xlsx", res.body)

That is the entire happy path. Everything below is refinement.

Sync or async

Two endpoints, one payload shape.

Send everything to /v1/workbooks until it tells you not to. Past your plan's cell limit it returns 413 naming /v1/jobs, so you do not have to guess where the line is.

Cells and types

A cell is a bare JSON value, or an object when it needs to be more.

["Widget", 1250.5, true, null]

[{"v": 1250.5, "s": "money"},
 {"f": "=SUM(B2:B10)", "result": 4820},
 {"v": "2026-08-06", "t": "date"},
 {"url": "https://example.com", "text": "invoice"}]

Styles

Declare once, reference by name. Repeating a font object per cell is the fastest way to turn a 20 MB request into a 200 MB one.

{
  "styles": {
    "header": {"font": {"bold": true}, "fill": {"color": "#1F2933"}},
    "money":  {"num_fmt": "#,##0.00"}
  },
  "sheets": [{
    "name": "Sales",
    "header_style": "header",
    "columns": [{"header": "Item"}, {"header": "Amount", "style": "money"}],
    "rows": [["Widget", 1250.5]],
    "freeze": {"row": 1, "col": 0},
    "autofilter": true
  }]
}

A cell's style beats its row's, which beats its column's. Styles do not merge. A cell gets exactly the style it names, so nothing inherits a border it never asked for.

Row forms

Three, all equivalent. Use whichever your data already is.

["Widget", 1250.5]                         // positional
{"Item": "Widget", "Amount": 1250.5}       // keyed by column
{"cells": ["Total", 4820], "style": "header"} // with row options

Keyed rows are placed by column order, not key order, so the two forms produce identical files.

Large exports

Send NDJSON to /v1/jobs: a header line describing the workbook, then one line per row. Nothing is ever held in full. A million rows costs tens of megabytes, not hundreds.

curl -X POST https://api.jarrah.sh/v1/jobs \
  -H "Authorization: Bearer $JARRAH_KEY" \
  -H "Content-Type: application/x-ndjson" \
  --data-binary @export.ndjson

# export.ndjson
{"sheets":[{"name":"Ledger","columns":[{"header":"Date"},{"header":"Amount"}]}]}
["2026-08-01", 120.00]
["2026-08-02", 98.50]

Then poll GET /v1/jobs/{id} until status is succeeded, or supply a webhook and be told.

Errors

Every error is RFC 7807 application/problem+json. Write the handling once.

{
  "type": "https://docs.jarrah.sh/errors/invalid-workbook",
  "title": "Workbook failed validation",
  "status": 422,
  "detail": "2 problem(s) found…",
  "errors": [
    {"pointer": "/sheets/0/name", "message": "sheet name contains '/'…"},
    {"pointer": "/sheets/0/rows/3/1", "message": "unknown style \"moneyy\"; did you mean \"money\"?"}
  ]
}

Every problem is reported at once, each located by a JSON Pointer into the body you sent. A generated payload gets fixed in one pass, not ten round trips.

Webhooks

Supply webhook on a job and we POST when it finishes, signed with your account secret.

X-Jarrah-Signature: t=1786044014,v1=5f3a…

The signature covers "<timestamp>.<body>". Verify against the raw bytes. Parsing and re-serialising changes key order and the signature will stop matching.

Three attempts, at 0s, 30s and 120s. A webhook we cannot deliver never fails your job. The file stays downloadable regardless.

Limits

A note on CSV

Add ?format=csv to get CSV instead. Cells beginning =, +, - or @ are prefixed with an apostrophe, because a CSV opened in a spreadsheet executes them. An attacker-supplied display name otherwise becomes code running on whoever opens your export. Pass ?escape_formulas=false only if the output is parsed rather than opened.