diff --git a/src/featureDetection.ts b/src/featureDetection.ts
index 76396eb..af36fbc 100644
--- a/src/featureDetection.ts
+++ b/src/featureDetection.ts
@@ -157,3 +157,26 @@ export async function detectContractFeatures(
 
   return features;
 }
+
+// === Fee-bump support
+
+/**
+ * Fee-bump transactions (CAP-0015) were introduced in Stellar protocol
+ * version 13. Networks on an older base protocol cannot process them.
+ */
+export const FEE_BUMP_MIN_PROTOCOL_VERSION = 13;
+
+/** Minimal network info needed to decide fee-bump availability. */
+export interface FeeBumpNetworkInfo {
+  /** The network's current base protocol version. */
+  protocolVersion: number;
+}
+
+/**
+ * Determine whether a network supports fee-bump transactions, based on its
+ * base protocol version. No network calls are made; pass a network info object
+ * (e.g. from Horizon's root endpoint or an RPC `getNetwork` response).
+ */
+export function detectFeeBumpSupport(networkInfo: FeeBumpNetworkInfo): boolean {
+  return networkInfo.protocolVersion >= FEE_BUMP_MIN_PROTOCOL_VERSION;
+}
diff --git a/src/flowVisualizer.ts b/src/flowVisualizer.ts
index 33a909f..9c9d2f4 100644
--- a/src/flowVisualizer.ts
+++ b/src/flowVisualizer.ts
@@ -3,6 +3,13 @@ import { InvoiceFlowFetcherNotRegisteredError } from "./errors.js";
 
 export type InvoiceFlowFetcher = (invoiceId: string) => Promise<Invoice>;
 
+export type FlowDiagramMode = "mermaid" | "ascii";
+
+export interface FlowDiagramOptions {
+  /** Output format. Defaults to "mermaid" (unchanged legacy behavior). */
+  mode?: FlowDiagramMode;
+}
+
 let invoiceFlowFetcher: InvoiceFlowFetcher | null = null;
 
 export function registerInvoiceFlowFetcher(fetcher: InvoiceFlowFetcher): void {
@@ -37,7 +44,8 @@ function allocatePayments(recipients: Recipient[], funded: bigint): Map<string,
 
 export async function generateFlowDiagram(
   invoiceId: string,
-  getInvoice?: InvoiceFlowFetcher
+  getInvoice?: InvoiceFlowFetcher,
+  options?: FlowDiagramOptions
 ): Promise<string> {
   const fetcher = getInvoice ?? invoiceFlowFetcher;
   if (!fetcher) {
@@ -45,11 +53,20 @@ export async function generateFlowDiagram(
   }
 
   const invoice = await fetcher(invoiceId);
-  const creatorId = nodeId("creator", invoice.creator);
-  const invoiceNodeId = nodeId("invoice", invoice.id);
   const totalPaid = invoice.payments.reduce((sum, payment) => sum + payment.amount, 0n);
   const funded = totalPaid > invoice.funded ? totalPaid : invoice.funded;
   const allocations = allocatePayments(invoice.recipients, funded);
+
+  if (options?.mode === "ascii") {
+    return renderAsciiDiagram(invoice, allocations);
+  }
+
+  return renderMermaidDiagram(invoice, allocations);
+}
+
+function renderMermaidDiagram(invoice: Invoice, allocations: Map<string, bigint>): string {
+  const creatorId = nodeId("creator", invoice.creator);
+  const invoiceNodeId = nodeId("invoice", invoice.id);
   const lines = [
     "flowchart LR",
     `  ${creatorId}["Creator: ${nodeLabel(invoice.creator)}"]`,
@@ -86,3 +103,22 @@ export async function generateFlowDiagram(
 
   return lines.join("\n");
 }
+
+// === ASCII rendering
+
+function renderAsciiDiagram(invoice: Invoice, allocations: Map<string, bigint>): string {
+  const lines = [
+    `[Creator: ${invoice.creator}]`,
+    `  --> [Invoice ${invoice.id}]`,
+  ];
+
+  for (const [index, recipient] of invoice.recipients.entries()) {
+    const paid = allocations.get(recipient.address) ?? 0n;
+    const status = paid >= recipient.amount ? "completed" : "pending";
+    lines.push(
+      `        --> [Recipient ${index + 1}: ${recipient.address}]  (${amountLabel(paid)} / ${amountLabel(recipient.amount)}) ${status}`
+    );
+  }
+
+  return lines.join("\n");
+}
diff --git a/test/featureDetection.test.ts b/test/featureDetection.test.ts
index cc0174a..762ea27 100644
--- a/test/featureDetection.test.ts
+++ b/test/featureDetection.test.ts
@@ -2,6 +2,7 @@ import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import {
   detectContractFeatures,
   clearFeatureCache,
+  detectFeeBumpSupport,
 } from "../src/featureDetection.js";
 import type { ContractFeatures } from "../src/types.js";
 
@@ -173,4 +174,16 @@ describe("detectContractFeatures", () => {
     // archival (5th, odd = ok) -> true
     expect(features.archival).toBe(true);
   });
+});
+
+describe("detectFeeBumpSupport", () => {
+  it("returns true for a network whose base protocol supports fee bumps", () => {
+    expect(detectFeeBumpSupport({ protocolVersion: 13 })).toBe(true);
+    expect(detectFeeBumpSupport({ protocolVersion: 21 })).toBe(true);
+  });
+
+  it("returns false for a network on a protocol older than fee-bump support", () => {
+    expect(detectFeeBumpSupport({ protocolVersion: 12 })).toBe(false);
+    expect(detectFeeBumpSupport({ protocolVersion: 10 })).toBe(false);
+  });
 });
\ No newline at end of file
diff --git a/test/flowVisualizer.test.ts b/test/flowVisualizer.test.ts
index f1d06d8..2622f80 100644
--- a/test/flowVisualizer.test.ts
+++ b/test/flowVisualizer.test.ts
@@ -30,4 +30,47 @@ describe("generateFlowDiagram", () => {
     expect(diagram).toContain("class recipient_1_GRECIPIENTA completed");
     expect(diagram).toContain("class recipient_2_GRECIPIENTB pending");
   });
+
+  it("renders a multi-line ASCII diagram with [label] nodes and --> edges when mode is 'ascii'", async () => {
+    const invoice: Invoice = {
+      id: "inv-1",
+      creator: "GCREATOR",
+      recipients: [
+        { address: "GRECIPIENTA", amount: 100n },
+        { address: "GRECIPIENTB", amount: 50n },
+      ],
+      token: "CUSDC",
+      deadline: 1_900_000_000,
+      funded: 120n,
+      status: "Pending",
+      payments: [{ payer: "GPAYER", amount: 120n }],
+    };
+
+    const diagram = await generateFlowDiagram("inv-1", async () => invoice, {
+      mode: "ascii",
+    });
+
+    expect(diagram.split("\n").length).toBeGreaterThan(1);
+    expect(diagram).toContain("[Creator: GCREATOR]");
+    expect(diagram).toContain("--> [Invoice inv-1]");
+    expect(diagram).toContain("--> [Recipient 1: GRECIPIENTA]  (100 / 100) completed");
+    expect(diagram).toContain("--> [Recipient 2: GRECIPIENTB]  (20 / 50) pending");
+    expect(diagram).not.toContain("flowchart LR");
+  });
+
+  it("defaults to Mermaid output when no mode is given", async () => {
+    const invoice: Invoice = {
+      id: "inv-1",
+      creator: "GCREATOR",
+      recipients: [{ address: "GRECIPIENTA", amount: 100n }],
+      token: "CUSDC",
+      deadline: 1_900_000_000,
+      funded: 100n,
+      status: "Pending",
+      payments: [{ payer: "GPAYER", amount: 100n }],
+    };
+
+    const diagram = await generateFlowDiagram("inv-1", async () => invoice);
+    expect(diagram).toContain("flowchart LR");
+  });
 });