Block Diagram

Back to Style Guide — Read the style guide first for emoji, color, and accessibility rules.

Syntax keyword: block-beta Best for: System block composition, layered architectures, component topology where spatial layout matters When NOT to use: Process flows (use Flowchart), infrastructure with cloud icons (use Architecture)

⚠️ Accessibility: Block diagrams do not support accTitle/accDescr. Always place a descriptive italic Markdown paragraph directly above the code block.

Exemplar Diagram

Block diagram showing a three-tier web application architecture from client-facing interfaces through application services to data storage, with emoji labels indicating component types:

mermaid

block-beta
    columns 3

    block:client:3
        columns 3
        browser["🌐 Browser"]
        mobile["📱 Mobile App"]
        cli["⌨️ CLI Tool"]
    end

    space:3

    block:app:3
        columns 3
        api["🖥️ API Server"]
        worker["⚙️ Worker"]
        cache["⚡ Redis Cache"]
    end

    space:3

    block:data:3
        columns 2
        db[("💾 PostgreSQL")]
        storage["📦 Object Storage"]
    end

    browser --> api
    mobile --> api
    cli --> api
    api --> worker
    api --> cache
    worker --> db
    api --> db
    worker --> storage

Tips

Use columns N to control the layout grid
Use space:N for empty cells (alignment/spacing)
Nest block:name:span { ... } for grouped sections
Connect blocks with --> arrows
Use emoji in labels ["🔧 Component"] for visual distinction
Use cylinder ("text") syntax for databases within blocks
Keep to 3–4 rows with 3–4 columns for readability
Always pair with a Markdown text description above for screen readers

Template

Description of the system layers and how components connect:

mermaid

block-beta
    columns 3

    block:layer1:3
        columns 3
        comp_a["📋 Component A"]
        comp_b["⚙️ Component B"]
        comp_c["📦 Component C"]
    end

    space:3

    block:layer2:3
        columns 2
        comp_d["💾 Component D"]
        comp_e["🔧 Component E"]
    end

    comp_a --> comp_d
    comp_b --> comp_d
    comp_c --> comp_e

Complex Example

Enterprise platform architecture rendered as a 5-tier block diagram with 15 components. Each tier is a block group spanning the full width, with internal columns controlling component layout. Connections show the primary data flow paths between tiers:

mermaid

block-beta
    columns 4

    block:clients:4
        columns 4
        browser["🌐 Browser"]
        mobile["📱 Mobile App"]
        partner["🔌 Partner API"]
        admin["🔐 Admin Console"]
    end

    space:4

    block:gateway:4
        columns 2
        apigw["🌐 API **Gateway**"]
        auth["🔐 Auth Service"]
    end

    space:4

    block:services:4
        columns 4
        user_svc["👤 User Service"]
        order_svc["📋 Order Service"]
        product_svc["📦 Product Service"]
        notify_svc["📤 Notification Service"]
    end

    space:4

    block:data:4
        columns 3
        postgres[("💾 PostgreSQL")]
        redis["⚡ Redis Cache"]
        elastic["🔍 Elasticsearch"]
    end

    space:4

    block:infra:4
        columns 3
        mq["📥 Message Queue"]
        logs["📊 Log Aggregator"]
        metrics["📊 Metrics Store"]
    end

    browser --> apigw
    mobile --> apigw
    partner --> apigw
    admin --> auth
    apigw --> auth
    apigw --> user_svc
    apigw --> order_svc
    apigw --> product_svc
    order_svc --> notify_svc
    user_svc --> postgres
    order_svc --> postgres
    product_svc --> elastic
    order_svc --> redis
    notify_svc --> mq
    order_svc --> mq
    mq --> logs

Why this works

5 tiers read top-to-bottom like a network diagram — clients, gateway, services, data, infrastructure. Each tier is a block spanning the full width with its own column layout.
space:4 creates visual separation between tiers without unnecessary lines or borders, keeping the diagram clean and scannable.
Cylinder syntax ("text") for databases — PostgreSQL renders as a cylinder, instantly recognizable as a data store. Other components use standard rectangles.
Connections show real data paths — not every possible connection, just the primary flows. A fully-connected diagram would be unreadable; this shows the key paths an engineer would trace during debugging.