The service id [ ] is already in use by another

Error message

The service id [${id}] is already in use by another ${this.registeredIds.get(id)}

What it means

Thrown by ArchitectureDB.addService when the service id already exists in registeredIds. The map stores every node/group id shared across services, junctions, and groups, so a collision with any prior entity (service, junction, or group) trips this. The suffix in the message ('node' or 'group') tells you which kind of entity already owns the id.

Solutions

Give each service a unique id; namespace ids if labels repeat.
Check db.getNode(id) / registeredIds before adding.
If the duplicate is intentional, alias via a different id and a title.

Example fix

// before
db.addService({ id: 'api', icon: 'foo' });
db.addService({ id: 'api', icon: 'bar' }); // throws

// after
db.addService({ id: 'api', icon: 'foo' });
db.addService({ id: 'api2', title: 'api', icon: 'bar' });

Defensive patterns

Strategy: validation

Validate before calling

function assertUnique(db: ArchitectureDB, id: string) {
  if (db.getNode(id)) throw new Error(`id '${id}' already exists`);
}
assertUnique(db, 'api');
db.addService({ id: 'api', icon: 'foo' });

Type guard

function isIdFree(db: ArchitectureDB, id: string): boolean {
  return db.getNode(id) === null;
}

Prevention

Namespace ids (e.g. 'svc_', 'j_', 'grp_') to avoid cross-type collisions.
Generate ids deterministically and dedupe before insertion.
Check db.getNode(id) before every add* call.

When it happens

Trigger: Defining two services with the same id; reusing a junction or group id as a service id; calling addService twice in a loop without unique ids.

Common situations: Generator producing duplicate ids, copy-pasted architecture blocks, or parsing user text where the same label maps to the same id twice.

Related errors

AI-assisted analysis of mermaid-js/mermaid@d93e9c88c0 (2026-08-12). Data as JSON: /api/errors/d2f527cd24d5faec. Report an issue: GitHub.

Appendix: source

Thrown at packages/mermaid/src/diagrams/architecture/architectureDb.ts:83

    this.groups = new Map();
    this.edges = [];
    this.layoutHints = [];
    this.registeredIds = new Map();
    this.dataStructures = undefined;
    this.elements = new Map();
    this.diagramId = '';
    commonClear();
  }

  public addService({
    id,
    icon,
    in: parent,
    title,
    iconText,
  }: Omit<ArchitectureService, 'edges'>): void {
    if (this.registeredIds.has(id)) {
      throw new Error(
        `The service id [${id}] is already in use by another ${this.registeredIds.get(id)}`
      );
    }
    if (parent !== undefined) {
      if (id === parent) {
        throw new Error(`The service [${id}] cannot be placed within itself`);
      }
      if (!this.registeredIds.has(parent)) {
        throw new Error(
          `The service [${id}]'s parent does not exist. Please make sure the parent is created before this service`
        );
      }
      if (this.registeredIds.get(parent) === 'node') {
        throw new Error(`The service [${id}]'s parent is not a group`);
      }
    }

    this.registeredIds.set(id, 'node');

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