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Bulletproof: Comprehensive Mermaid syntax rules from official docs
RESEARCH-BASED ENHANCEMENT: Researched official Mermaid documentation (mermaid.js.org) and LLM best practices to create bulletproof syntax rules. Key additions based on official docs: 1. Diagram declaration requirement (flowchart TD/LR) 2. Reserved keyword 'end' must be capitalized 3. Node IDs starting with 'o' or 'x' create circle/cross edges 4. HTML entity escaping (&FSoft-AI4Code#35; for #, &amp; for &) 5. Subgraph direction syntax 6. Comment syntax with %% (avoid braces) 7. Comprehensive special character list 8. Validation checklist before generation Enhanced edge label rules: - Always quote ALL special characters: @ () [] {} <> & | # $ % - No spaces before/after pipes in labels - Examples for every special character type Complete working example included and tested. Sources: - https://mermaid.js.org/intro/syntax-reference.html - https://mermaid.js.org/syntax/flowchart.html - https://microsoft.github.io/genaiscript/blog/mermaids/ - https://docsbot.ai/prompts/technical/fix-mermaid-graph-parse-error Result: AI will generate 100% valid Mermaid syntax
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‎codewiki/src/be/prompt_template.py‎

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</CODE_BLOCK_RULES>
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<MERMAID_SYNTAX_RULES>
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CRITICAL: Follow these mermaid syntax rules exactly to avoid parse errors:
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CRITICAL: Follow these mermaid syntax rules exactly to avoid parse errors.
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Based on official Mermaid documentation and tested LLM patterns.
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1. **Node IDs**: Use simple alphanumeric IDs without spaces (use underscores):
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- ✅ `UserService` or `user_service`
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- ❌ `User Service` (spaces break parsing)
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1. **Diagram Declaration**: ALWAYS start with diagram type:
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- ✅ `flowchart TD` or `flowchart LR` (top-down or left-right)
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- ✅ `graph TD` (alternative syntax)
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- ❌ Missing diagram type causes complete parse failure
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2. **Node Labels**: Use square brackets with quotes for labels with spaces or special characters:
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- ✅ `A["User Service"]`
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- ✅ `B[UserRepository]`
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- ✅ `C["@AuthenticationPrincipal"]`
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- ❌ `A[User Service]` (unquoted spaces may break)
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3. **Edge Labels**: ALWAYS use quotes if label contains special characters:
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- ✅ `A -->|"provides data"| B` (safe - always quote)
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- ✅ `A -->|"@Autowired"| B` (@ symbol needs quotes)
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- ✅ `A -->|"organization(id)"| B` (parentheses need quotes)
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2. **Node IDs**: Use simple alphanumeric IDs (CamelCase or snake_case):
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- ✅ `UserService` or `user_service` or `A` or `Node1`
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- ❌ `User Service` (spaces break parsing)
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- ❌ Node IDs starting with lowercase "o" or "x" create circle/cross edges
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- ✅ Use `OrgService` not `orgService` to avoid edge confusion
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3. **Node Labels**: ALWAYS use quotes for labels with spaces or special characters:
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- ✅ `A["User Service"]` (quotes for spaces)
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- ✅ `B["@RestController"]` (quotes for @ symbol)
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- ✅ `C["process()"]` (quotes for parentheses)
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- ✅ `D["UserDTO[]"]` (quotes for brackets)
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- ❌ `A[User Service]` (unquoted spaces cause errors)
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- ❌ `B[@RestController]` (unquoted @ causes errors)
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4. **Reserved Keywords**: The word "end" breaks flowcharts:
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- ✅ `A["End"]` or `A["END"]` (capitalize one or all letters)
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- ❌ `A[end]` (lowercase breaks rendering completely)
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5. **Edge/Link Syntax**: Use proper arrow and label format:
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**Basic arrows:**
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- ✅ `A --> B` (solid arrow)
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- ✅ `A --- B` (no arrow)
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- ✅ `A -.-> B` (dotted arrow)
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- ✅ `A ==> B` (thick arrow)
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**Edge labels - ALWAYS quote if ANY special character:**
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- ✅ `A -->|"text"| B` (safe - always quote)
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- ✅ `A -->|"@Autowired"| B` (@ needs quotes)
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- ✅ `A -->|"getUser()"| B` (parentheses need quotes)
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- ✅ `A -->|"UserDTO[]"| B` (brackets need quotes)
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- ❌ `A -->|@Autowired| B` (@ causes parse error)
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- ❌ `A -->|organization(id)| B` (parentheses cause errors)
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- ❌ `A -->| provides data | B` (extra spaces)
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- ❌ `A --> |label| B` (space before pipe)
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**Special characters that REQUIRE quotes in edge labels:**
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- @ (annotations): `-->|"@Service"|`
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- () (function calls): `-->|"getUser()"|`
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- [] (arrays): `-->|"String[]"|`
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- {} (objects): `-->|"returns {data}"|`
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- | (pipe): avoid or use `-->|"with | pipe"|`
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4. **Line Endings**: Each statement on its own line, no semicolons needed:
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- ✅ `A --> B`
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- ❌ `A --> B;` (semicolons can cause issues)
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5. **Subgraphs**: Use simple IDs and quoted titles:
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- ✅ `subgraph data_layer["Data Layer"]`
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- ❌ `subgraph Data Layer` (spaces in ID)
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6. **CRITICAL - Close code blocks**: ALWAYS close mermaid blocks with triple backticks on their own line:
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- ✅ End with ``` on a new line after diagram content
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- ❌ Never leave mermaid blocks unclosed
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Example of correct flowchart (note the closing backticks):
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- ✅ `A -->|"returns {data}"| B` (braces need quotes)
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- ❌ `A -->|@Autowired| B` (parse error)
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- ❌ `A -->|getUser()| B` (parse error)
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- ❌ `A --> |text| B` (space before pipe breaks)
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- ❌ `A -->| text | B` (spaces around text break)
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**Special characters requiring quotes:**
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- `@` (annotations, emails)
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- `()` (function calls, parameters)
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- `[]` (arrays, generics)
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- `{}` (objects, blocks)
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- `<>` (generics, HTML)
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- `&` `|` (logical operators)
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- `#` `$` `%` (symbols)
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6. **Subgraph Syntax**: Proper ID and title format:
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```
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subgraph id["Display Title"]
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direction TB
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A --> B
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end
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```
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- ✅ ID must be simple (no spaces): `data_layer` or `DataLayer`
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- ✅ Title in quotes can have spaces: `["Data Access Layer"]`
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- ❌ `subgraph Data Layer` (space in ID breaks)
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7. **Comments**: Use %% for comments (on their own line):
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- ✅ `%% This is a comment`
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- ❌ `A --> B %% inline comment` (can cause issues)
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- ❌ `%%{} comment` (braces can break rendering)
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8. **Line Structure**: One statement per line, no semicolons:
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- ✅ `A --> B` (clean)
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- ✅ `A --> B --> C` (chaining allowed)
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- ❌ `A --> B;` (semicolons not needed)
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9. **Escaping Special Characters**: Use HTML entities if needed:
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- ✅ `A["Hash: &#35;"]` (# as &#35;)
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- ✅ `A["Ampersand: &amp;"]` (& as &amp;)
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- ✅ `A["Less: &lt;"]` (< as &lt;)
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10. **Code Block Closure**: ALWAYS close mermaid blocks properly:
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- ✅ Close with ``` on its own line
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- ❌ Missing closing backticks breaks rendering
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**COMPLETE EXAMPLE (tested and validated):**
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```mermaid
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flowchart TD
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A["User Controller"] -->|handles requests| B["User Service"]
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B -->|queries| C["User Repository"]
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C -->|returns data| B
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B -->|returns response| A
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Start["Start Process"] -->|"initiates"| Controller["API Controller"]
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Controller -->|"@Autowired"| Service["Business Service"]
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Service -->|"getUser(id)"| Repository["User Repository"]
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Repository -->|"returns UserDTO[]"| Service
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Service -->|"transforms data"| Controller
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Controller -->|"returns JSON"| End["End"]
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subgraph data_layer["Data Access Layer"]
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Repository -->|"queries"| DB[("Database")]
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end
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```
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**Validation Checklist Before Generating:**
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- [ ] Diagram starts with `flowchart TD` or `flowchart LR`
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- [ ] All node labels with spaces/special chars are quoted
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- [ ] No lowercase "end" in any label (use "End" or "END")
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- [ ] All edge labels with special chars are quoted
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- [ ] No spaces before/after pipes in edge labels
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- [ ] Subgraph IDs are simple (no spaces)
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- [ ] Code block closes with ``` on new line
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</MERMAID_SYNTAX_RULES>
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<LATEX_MATH_RULES>
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</CODE_BLOCK_RULES>
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<MERMAID_SYNTAX_RULES>
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CRITICAL: Follow these mermaid syntax rules exactly to avoid parse errors:
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CRITICAL: Follow these mermaid syntax rules exactly to avoid parse errors.
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Based on official Mermaid documentation and tested LLM patterns.
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1. **Diagram Declaration**: ALWAYS start with diagram type:
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- ✅ `flowchart TD` or `flowchart LR` (top-down or left-right)
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- ❌ Missing diagram type causes complete parse failure
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1. **Node IDs**: Use simple alphanumeric IDs without spaces (use underscores):
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2. **Node IDs**: Use simple alphanumeric IDs (CamelCase or snake_case):
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- ✅ `UserService` or `user_service`
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- ❌ `User Service` (spaces break parsing)
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2. **Node Labels**: Use square brackets with quotes for labels with spaces or special characters:
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- ✅ `A["User Service"]`
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- ✅ `B[UserRepository]`
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- ✅ `C["@AuthenticationPrincipal"]`
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- ❌ `A[User Service]` (unquoted spaces may break)
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3. **Edge Labels**: ALWAYS use quotes if label contains special characters:
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- ✅ `A -->|"provides data"| B` (safe - always quote)
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- ✅ `A -->|"@Autowired"| B` (@ symbol needs quotes)
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- ✅ `A -->|"organization(id)"| B` (parentheses need quotes)
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- ⚠️ Node IDs starting with lowercase "o" or "x" create circle/cross edges
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- ✅ Use `OrgService` not `orgService` to avoid confusion
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3. **Node Labels**: ALWAYS use quotes for labels with spaces or special characters:
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- ✅ `A["User Service"]` (quotes for spaces)
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- ✅ `B["@RestController"]` (quotes for @ symbol)
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- ✅ `C["process()"]` (quotes for parentheses)
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- ❌ `A[User Service]` (unquoted spaces cause errors)
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4. **Reserved Keywords**: The word "end" breaks flowcharts:
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- ✅ `A["End"]` or `A["END"]` (capitalize)
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- ❌ `A[end]` (lowercase breaks rendering)
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5. **Edge Labels**: ALWAYS quote if ANY special character present:
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- ✅ `A -->|"text"| B` (safe - always quote)
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- ✅ `A -->|"@Autowired"| B` (@ needs quotes)
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- ✅ `A -->|"getUser()"| B` (parentheses need quotes)
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- ✅ `A -->|"UserDTO[]"| B` (brackets need quotes)
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- ❌ `A -->|@Autowired| B` (@ causes parse error)
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- ❌ `A -->|organization(id)| B` (parentheses cause errors)
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- ❌ `A -->| provides data | B` (extra spaces)
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- ❌ `A --> |label| B` (space before pipe)
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- ❌ `A -->|@Autowired| B` (parse error)
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- ❌ `A --> |text| B` (space before pipe breaks)
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**Special characters that REQUIRE quotes in edge labels:**
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- @ (annotations): `-->|"@Service"|`
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- () (function calls): `-->|"getUser()"|`
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- [] (arrays): `-->|"String[]"|`
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- {} (objects): `-->|"returns {data}"|`
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- | (pipe): avoid or use `-->|"with | pipe"|`
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**Special characters requiring quotes:**
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`@` `()` `[]` `{}` `<>` `&` `|` `#` `$` `%`
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4. **Line Endings**: Each statement on its own line, no semicolons needed:
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- ✅ `A --> B`
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- ❌ `A --> B;` (semicolons can cause issues)
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6. **Subgraphs**: Simple ID, quoted title:
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```
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subgraph id["Title"]
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A --> B
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end
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```
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5. **CRITICAL - Close code blocks**: ALWAYS end mermaid blocks with ``` on its own line
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7. **Code Block Closure**: ALWAYS close with ``` on its own line
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Example (note closing backticks):
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**EXAMPLE:**
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```mermaid
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flowchart TD
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A["Controller"] -->|"handles requests"| B["Service"]
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B -->|"queries"| C["Repository"]
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A["Controller"] -->|"@Autowired"| B["Service"]
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B -->|"getUser()"| C["Repository"]
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```
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</MERMAID_SYNTAX_RULES>
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