Diagram API

The ChartQuery Diagram API renders diagram-as-code (Mermaid, Graphviz, PlantUML, D2 and 24 other languages) to PNG, SVG, JPEG or PDF — or generates a diagram from a plain-English prompt.

• Diagram Render API — Render a diagram via GET.
• AI Diagram API — Describe a diagram in plain English via GET and get a rendered image back.

Use it for docs, READMEs, wikis, architecture diagrams and AI assistants.

Endpoint	Request	Credits
Diagram Render API	GET /v1/diagram	5
AI Diagram API	GET /v1/diagram/ai	10

Table of contents

• How it works
• Diagram Render API
• AI Diagram API
• Code examples in other languages
• Use cases
• Why ChartQuery?
• FAQ
• Related repositories
• Support

How it works

1. Create a ChartQuery account and copy your API key from the dashboard.
2. Call https://api.chartquery.com with the header x-api-key: YOUR_API_KEY.
3. Use the result in your app — no infrastructure to run.

export CHARTQUERY_API_KEY="your-api-key"
pip install requests        # Python
# TypeScript: Node.js 18+ (native fetch), run with `npx tsx file.ts`

Diagram Render API

Render a diagram via GET. Use type (mermaid, d2, …), query (source code), and format=png for ChatGPT. POST uses diagram_type and diagram_source instead.

GET https://api.chartquery.com/v1/diagram · 5 credits per request · API reference

Request parameters

Parameter	In	Type	Required	Description
type	query	string (mermaid, graphviz, plantuml, d2, svgbob, nomnoml)	✅	Diagram language.
query	query	string	✅	Diagram source code (URL-encoded).
format	query	string (svg, png, jpeg, pdf)	—	Use png so ChatGPT can display the image. svg is for download or infinite scale.
share	query	boolean	—	If true, persist the result and return share URLs instead of an image. Leave false to get the image.

Python example

import os

import requests

API_KEY = os.environ["CHARTQUERY_API_KEY"]
HEADERS = {"x-api-key": API_KEY}

response = requests.get(
    "https://api.chartquery.com/v1/diagram",
    headers=HEADERS,
    params={
        "type": "mermaid",
        "query": "graph TD\n  A[Start] --> B{OK?}\n  B -->|yes| C[End]\n  B -->|no| D[Error]",
        "format": "png",
    },
    timeout=120,
)
response.raise_for_status()

with open("diagram.png", "wb") as f:
    f.write(response.content)
print("Saved diagram.png", len(response.content), "bytes")

TypeScript example

import { writeFile } from "node:fs/promises";

const headers = { "x-api-key": process.env.CHARTQUERY_API_KEY!, "Content-Type": "application/json" };

const params = new URLSearchParams({
  "type": "mermaid",
  "query": "graph TD\n  A[Start] --> B{OK?}\n  B -->|yes| C[End]\n  B -->|no| D[Error]",
  "format": "png",
});

const response = await fetch(`https://api.chartquery.com/v1/diagram?${params}`, { headers });
if (!response.ok) throw new Error(`HTTP ${response.status}: ${await response.text()}`);

await writeFile("diagram.png", Buffer.from(await response.arrayBuffer()));
console.log("Saved diagram.png");

Output

The response body is the generated file (saved as diagram.png in every example). Error responses are JSON with an explanatory message.

AI Diagram API

Describe a diagram in plain English via GET and get a rendered image back. Powered by AI.

GET https://api.chartquery.com/v1/diagram/ai · 10 credits per request · API reference

Request parameters

Parameter	In	Type	Required	Description
prompt	query	string	✅	Describe your diagram in plain English (max 1000 chars). Be specific: mention the diagram type, key entities, and relationships.
diagram_type	query	string (mermaid, d2, plantuml, graphviz)	—	Preferred diagram language. AI chooses if omitted. Examples: "mermaid", "d2", "plantuml", "graphviz".
output_format	query	string (svg, png, jpeg, pdf)	—	Output format. Default: "svg".
share	query	boolean (false, true)	—	Set share=true to persist the config and receive JSON instead of an image: { id, render_url, view_url, embed_url, expires_in }. Free plan: 3-day expiry. Paid plan: 6-month expiry.

Python example

import os

import requests

API_KEY = os.environ["CHARTQUERY_API_KEY"]
HEADERS = {"x-api-key": API_KEY}

response = requests.get(
    "https://api.chartquery.com/v1/diagram/ai",
    headers=HEADERS,
    params={
        "prompt": "Sequence diagram of a user logging in through an API gateway to an auth service",
        "output_format": "png",
    },
    timeout=120,
)
response.raise_for_status()

with open("ai-diagram.png", "wb") as f:
    f.write(response.content)
print("Saved ai-diagram.png", len(response.content), "bytes")

TypeScript example

import { writeFile } from "node:fs/promises";

const headers = { "x-api-key": process.env.CHARTQUERY_API_KEY!, "Content-Type": "application/json" };

const params = new URLSearchParams({
  "prompt": "Sequence diagram of a user logging in through an API gateway to an auth service",
  "output_format": "png",
});

const response = await fetch(`https://api.chartquery.com/v1/diagram/ai?${params}`, { headers });
if (!response.ok) throw new Error(`HTTP ${response.status}: ${await response.text()}`);

await writeFile("ai-diagram.png", Buffer.from(await response.arrayBuffer()));
console.log("Saved ai-diagram.png");

Output

The response body is the generated file (saved as ai-diagram.png in every example). Error responses are JSON with an explanatory message.

Code examples in other languages

Ready-to-run examples live in examples/; each reads your key from CHARTQUERY_API_KEY.

Language	diagram	diagram-ai
cURL (Bash)	diagram.sh	diagram_ai.sh
PHP	diagram.php	diagram_ai.php
C#	Diagram.cs	DiagramAi.cs
Go	diagram.go	diagram_ai.go
Java	DiagramExample.java	DiagramAiExample.java
Ruby	diagram.rb	diagram_ai.rb
Node.js	diagram.mjs	diagram_ai.mjs

Use cases

• Documentation — Render diagrams for docs and wikis on the fly.
• Architecture — Keep diagrams as code and render them in CI.
• AI assistants — Let agents draw flowcharts and sequence diagrams.

Why ChartQuery?

• Images in one request — the response body is the PNG/SVG/PDF, ready for emails, PDFs, dashboards, Slack or <img> tags.
• Charts, diagrams, QR codes, barcodes, labels — Chart.js configs, 28 diagram languages (Mermaid, Graphviz, PlantUML, D2…), 25+ barcode formats.
• AI generation — describe a chart or diagram in plain English and get the rendered image.
• No rendering infrastructure — no headless browser, fonts or libraries to maintain.
• Copy-paste examples — Python and TypeScript in each README, 7 more languages in examples/.

FAQ

How do I authenticate?

Create an account on ChartQuery, copy your API key and send it in the x-api-key header of every request to https://api.chartquery.com.

How much does a request cost?

Credits per call: /v1/diagram 5, /v1/diagram/ai 10. See ChartQuery pricing.

What does the API return?

The response body is the file itself (image or document). Save it directly to disk or stream it to your storage — every example in this repository writes the file locally.

Which diagram languages are supported?

mermaid, graphviz, plantuml, d2, svgbob, nomnoml, blockdiag, seqdiag, actdiag, nwdiag, bpmn, erd, excalidraw, ditaa, vega, vegalite, wavedrom, wireviz, c4plantuml, structurizr, tikz, pikchr, umlet, symbolator, packetdiag, rackdiag, bytefield and dbml.

Which languages are supported?

Any language that can make an HTTP request. This README shows Python and TypeScript; the examples/ folder contains cURL, PHP, C#, Go, Java, Ruby and Node.js.

Related repositories

• Chart API
• QR Code API
• Barcode API
• Thermal Label API
• All ChartQuery repositories

Support

• 💬 Join the Discord to ask questions and share what you build.
• 📚 Read the API reference.
• 🔑 Get your API key.

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_{Built by ChartQuery. Examples are released under the MIT license.}