mermaid-js/mermaid · error

align lists [ ] more than once

Error message

align ${hint.direction} lists [${id}] more than once

What it means

Thrown by ArchitectureDB.addLayoutHint when the same id appears more than once in hint.members. The DB walks the members array with a `seen` Set and rejects any repeat. An align chain with a duplicated node would create a degenerate (zero-length) constraint and confuse the layout engine.

Solutions

1. Remove duplicate ids so each member appears exactly once.
2. Dedupe the members array before calling addLayoutHint.

Example fix

// before
db.addLayoutHint({ direction: 'row', members: ['a', 'a', 'b'] });
// after
db.addLayoutHint({ direction: 'row', members: ['a', 'b'] });

function addLayoutHintSafe(db, hint) {
  if (new Set(hint.members).size !== hint.members.length) {
    throw new Error('align members contains duplicates');
  }
  db.addLayoutHint(hint);
}

const hasNoDuplicates = (arr) => new Set(arr).size === arr.length;

When it happens

Trigger: Calling db.addLayoutHint({ direction: 'row', members: ['a', 'a', 'b'] }). In DSL: `align row: a, a, b`.

Common situations: Copy-paste duplication in a DSL align chain; programmatic array construction that concatenates lists without dedup; refactors that merge two align directives naively.

Related errors

• align references [ ], which is not a service or junction
• An align directive requires at least two members; got
• Architecture layout failed: a declared `align row|column`…
• Both layout algorithms
• Columns must be an integer !== 0.

AI-assisted analysis of mermaid-js/mermaid@d93e9c88c0 (2026-08-12). Data as JSON: /api/errors/7da669a73f08fbca. Report an issue: GitHub.

Appendix: source

Thrown at packages/mermaid/src/diagrams/architecture/architectureDb.ts:277

  public getEdges(): ArchitectureEdge[] {
    return this.edges;
  }

  public addLayoutHint(hint: ArchitectureLayoutHint): void {
    if (hint.members.length < 2) {
      throw new Error(
        `An align directive requires at least two members; got ${hint.members.length}`
      );
    }
    const seen = new Set<string>();
    hint.members.forEach((id) => {
      if (this.registeredIds.get(id) !== 'node') {
        throw new Error(
          `align ${hint.direction} references [${id}], which is not a service or junction`
        );
      }
      if (seen.has(id)) {
        throw new Error(`align ${hint.direction} lists [${id}] more than once`);
      }
      seen.add(id);
    });
    this.layoutHints.push(hint);
  }

  public getLayoutHints(): ArchitectureLayoutHint[] {
    return this.layoutHints;
  }

  /**
   * Returns the current diagram's adjacency list, spatial map, & group alignments.
   * If they have not been created, run the algorithms to generate them.
   * @returns
   */
  public getDataStructures() {
    if (this.dataStructures === undefined) {
      // Tracks how groups are aligned with one another. Generated while creating the adj list

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