Mermaid vs AWS Application Composer: which should you use for AWS architecture diagrams?
AWS Application Composer (now Infrastructure Composer) builds and deploys infrastructure; Mermaid architecture-beta diagrams document and communicate it. A side-by-side comparison of what each is for, where each wins, and the workflow that uses both together — with a validated Mermaid example.
AWS Application Composer (now AWS Infrastructure Composer) is a visual builder that generates deployable CloudFormation and SAM templates — reach for it to author and ship AWS infrastructure. Mermaid architecture-beta diagrams, validated in LatixEngine, are text-based diagrams-as-code for documenting and reviewing architecture across any cloud. They solve different problems, and most teams use both.
If you draw AWS architectures, you eventually hit the question: should you use AWS Application Composer (renamed AWS Infrastructure Composer in 2024) or a text-based diagram-as-code tool like Mermaid? They look like competitors — both put boxes and arrows on a screen — but they belong to different categories and answer different questions. Application Composer is a tool for building infrastructure. Mermaid is a format for documenting it.
Picking the wrong one wastes time in both directions: teams try to use Application Composer as a living architecture doc and find it only ever shows one deployable stack, or they hand-draw diagrams they then struggle to keep truthful. This post lays out what each tool is actually for, where each one wins, and the workflow that uses both together. If you are brand new to the Mermaid side, start with how to draw AWS architecture diagrams in Mermaid; for a comparison against GUI editors like draw.io and Lucidchart specifically, that post has a dedicated table.
Use Application Composer when your goal is to provision resources — it generates deployable IaC. Use Mermaid diagrams-as-code when your goal is to explain a system to people across any cloud, in docs that live in git and can be validated. The two are complementary, not either/or.
What is AWS Application Composer?
AWS Application Composer is a visual designer, built into the AWS Management Console and available locally in VS Code through the AWS Toolkit, for authoring infrastructure as code. You drag AWS resources onto a canvas, connect them, and the tool generates and round-trips CloudFormation and AWS SAM templates. Edit the canvas and the template updates; edit the template and the canvas follows.
Its center of gravity is serverless and event-driven building blocks — Lambda functions, API Gateway, DynamoDB tables, Step Functions, EventBridge, and SQS/SNS — though it can represent a broad range of CloudFormation resource types. The output is not a picture; it is a deployable artifact. That is the whole point: the diagram is the template, and the template ships to AWS.
Because it is anchored to CloudFormation, Application Composer is AWS-only, and the canvas is scoped to what a single stack deploys. It is excellent at what it is designed for — turning an idea into provisionable infrastructure quickly — and it is free; you pay only for the resources you actually deploy.
What are Mermaid architecture-beta diagrams?
Mermaid is a diagram-as-code language: you describe a diagram in plain text and a renderer draws it. Its architecture-beta diagram type is purpose-built for cloud architecture — groups for accounts, regions, VPCs, and subnets; services for individual resources; and port-based edges for the wiring. LatixEngine renders that syntax with 856 native AWS icons (1698 across AWS, Azure, and GCP) and, crucially, validates the result against each provider's rules and Well-Architected best practices.
The source is text, so it lives beside your code, diffs cleanly in a pull request, and renders identically on any machine with no install or login. Here is a serverless API as Mermaid architecture-beta — the same category of system Application Composer specializes in, but expressed for documentation:
architecture-beta
service users(aws:res-users-light)[Users]
group aws_account(aws:aws-account)[AWS Account]
group region(aws:region)[us-east-1] in aws_account
service apigw(aws:arch-amazon-api-gateway)[API Gateway] in region
service ddb(aws:arch-amazon-dynamodb)[DynamoDB] in region
group vpc(aws:virtual-private-cloud-vpc)[VPC] in region
group priv(aws:private-subnet)[Private Subnet] in vpc
service fn(aws:arch-aws-lambda)[Lambda] in priv
users:R <--> L:apigw
apigw:B <--> T:fn
fn:R <--> L:ddbUnlike Application Composer, this diagram does not deploy anything. That is a feature, not a gap: it can show cross-account context, non-AWS systems, and a whole platform's shape without being tied to one stack — and it can be checked for correctness before anyone reads it. For the grammar behind the ports and edges, see the architecture-beta syntax reference.
Mermaid vs AWS Application Composer: a side-by-side comparison
The clearest way to choose is to line up what each tool optimizes for. They overlap only at the surface.
| Dimension | AWS Application Composer | Mermaid architecture-beta (LatixEngine) |
|---|---|---|
| Primary purpose | Build and deploy AWS infrastructure | Document and communicate architecture |
| Output | CloudFormation / SAM templates + canvas | Mermaid text → SVG, PNG, or markdown |
| Source of truth | Visual canvas ↔ IaC template | Plain-text diagram versioned in git |
| Cloud coverage | AWS only | AWS, Azure, and GCP |
| Where it runs | AWS Console + VS Code (AWS Toolkit) | Any browser — no login, no install |
| Deploys infrastructure? | Yes, via CloudFormation | No — documentation only |
| What it validates | Template / CloudFormation validity | Architecture rules + Well-Architected best practices |
| Scope of a view | One deployable stack | Whole system, multi-account, multi-cloud |
| Best fit | Provisioning serverless / IaC resources | Docs, RFCs, PRs, reviews, onboarding |
| Cost | Free; pay for deployed resources | Free; nothing to deploy or bill |
When should you use AWS Application Composer?
Reach for Application Composer when the deliverable is running infrastructure, not a document. It is the right tool when you are:
- Prototyping a serverless application and want deployable CloudFormation or SAM without hand-writing YAML.
- Working inside the AWS ecosystem and want the canvas and template to stay in sync as you iterate.
- Standing up a single stack quickly and deploying it from the same surface you designed it on.
In these cases the diagram is a means to an end — the template — and Application Composer's tight coupling to CloudFormation is exactly what you want.
When should you use Mermaid diagram-as-code?
Reach for Mermaid when the deliverable is understanding. It is the right tool when you are:
- Writing docs, RFCs, or design reviews that need to explain a system, not deploy it.
- Diagramming across accounts, regions, or clouds — or including non-AWS components a CloudFormation stack cannot represent.
- Keeping architecture diagrams truthful over time by versioning them as text next to the code they describe.
- Checking a design against best practices — LatixEngine flags public databases, single-AZ deployments, API Gateway wired straight to a relational database, and more. See common AWS architecture mistakes for the full catalogue, and the patterns gallery for copy-paste starting points.
The trade-off is direct: Application Composer gives you something you can deploy; Mermaid gives you something people (and AI engines) can read, review, and trust.
Can you use AWS Application Composer and Mermaid together?
Yes — and for most teams that is the best answer. The two tools sit at different stages of the same lifecycle. Application Composer helps you build a stack; Mermaid helps you explain the system that stack is part of.
A common pairing looks like this: design and deploy individual stacks in Application Composer, then maintain a Mermaid architecture-beta diagram as the durable, human-facing picture of the whole platform — the one that goes in the README, the onboarding guide, and the design doc. The template deploys; the diagram communicates. Neither has to pretend to be the other.
How do you turn an Application Composer design into a Mermaid diagram?
When you want to promote a Composer-built stack into your documentation, you do not have to redraw it by hand:
- Copy or export the CloudFormation / SAM template Application Composer generated.
- Hand it to ChatGPT, Claude, or Gemini using the grounding pattern from how to prompt LLMs for Mermaid AWS diagrams — this is where models reliably hallucinate icon slugs, and the pattern fixes it.
- Paste the generated Mermaid into LatixEngine. It flags any invalid slugs against the icon catalog and validates placement, so what lands in your docs is correct.
- Commit the .mmd text alongside your code and render it wherever you publish — see rendering and embedding Mermaid AWS diagrams.
That bridge lets Application Composer do what it is best at — building and deploying — while your documentation stays in a portable, validated, multi-cloud format that outlives any single template. LatixEngine is free, runs in the browser, and needs no login to validate and export your diagrams.
Frequently asked questions
What is the difference between Mermaid and AWS Application Composer?
AWS Application Composer is an infrastructure-authoring tool: you drag resources onto a canvas and it produces deployable CloudFormation or SAM templates. Mermaid architecture-beta is a documentation format: you write plain text and it renders a diagram you version in git, review in a PR, and validate for best practices. One builds infrastructure; the other explains it.
Does AWS Application Composer replace architecture diagrams?
No. Application Composer's canvas mirrors a deployable template, so it shows the resources in one stack — not the wider system context, cross-account boundaries, or non-AWS pieces. A dedicated diagram-as-code layer like Mermaid stays useful for docs, RFCs, and onboarding that outlive any single template.
Can AWS Application Composer draw Azure or GCP architectures?
No. Application Composer is AWS-only and works against CloudFormation and SAM. Mermaid architecture-beta in LatixEngine ships native icons for AWS, Azure, and GCP, so a single diagram format covers multi-cloud and hybrid systems.
Is AWS Application Composer free?
Application Composer is free to use; you pay only for the AWS resources you actually deploy from the templates it generates. LatixEngine is also free, with no login or install, and runs entirely in the browser — it never provisions anything, so there is nothing to bill for.
Should I use Application Composer or Mermaid for documentation?
Use Mermaid for documentation. Application Composer is optimized for building and deploying a stack, not for explaining a system to people. Mermaid diagrams live next to your code as plain text, render on any machine, and can be validated against AWS rules before you publish them.
How do I turn an Application Composer design into a Mermaid diagram?
Export or copy the CloudFormation/SAM template Application Composer generates, hand it to an LLM with the grounding pattern from our prompting guide, and it will produce Mermaid architecture-beta source. Paste that into LatixEngine to fix any hallucinated icon slugs and validate placement before you commit it.
Paste any example in this post into the LatixEngine editor to render it with native cloud icons and validate it against AWS, Azure, and GCP best practices. No login, no install.
Open the editor →