diff --git a/src/experience-tracker.ts b/src/experience-tracker.ts
index 3ae2b6e..7560815 100644
--- a/src/experience-tracker.ts
+++ b/src/experience-tracker.ts
@@ -8,6 +8,7 @@ import { KnowledgeTracker } from './knowledge-tracker.js';
 import type { WebPageState } from './state-manager.js';
 import { createDebug, tag } from './utils/logger.js';
 import { mdq } from './utils/markdown-query.js';
+import { redactSecrets } from './utils/secrets.js';
 import { isNonReusableCode } from './utils/step-analyzer.ts';
 import { extractStatePath } from './utils/url-matcher.js';
 
@@ -109,7 +110,7 @@ export class ExperienceTracker {
       return;
     }
     const filePath = this.getExperienceFilePath(stateHash);
-    const fileContent = matter.stringify(content, frontmatter || {});
+    const fileContent = matter.stringify(redactSecrets(content), frontmatter || {});
     writeFileSync(filePath, fileContent, 'utf8');
   }
 
diff --git a/src/knowledge-tracker.ts b/src/knowledge-tracker.ts
index d37ed9c..44d4b67 100644
--- a/src/knowledge-tracker.ts
+++ b/src/knowledge-tracker.ts
@@ -5,6 +5,7 @@ import { ActionResult } from './action-result.js';
 import { ConfigParser } from './config.js';
 import { getCliName } from './utils/cli-name.ts';
 import { createDebug } from './utils/logger.js';
+import { isSecretName, registerSecret } from './utils/secrets.js';
 
 const debugLog = createDebug('explorbot:knowledge-tracker');
 
@@ -138,9 +139,14 @@ export class KnowledgeTracker {
       const namespace = expr.slice(0, dotIndex);
       const key = expr.slice(dotIndex + 1);
 
-      if (namespace === 'env') return process.env[key] ?? '';
+      if (namespace === 'env') {
+        const value = process.env[key] ?? '';
+        if (isSecretName(key)) registerSecret(value);
+        return value;
+      }
 
       if (namespace === 'config') {
+        if (isSecretName(key)) return '';
         const config = ConfigParser.getInstance().getConfig();
         const value = key.split('.').reduce((obj: any, k) => obj?.[k], config);
         if (value !== undefined && typeof value !== 'object') return String(value);
diff --git a/src/observability.ts b/src/observability.ts
index bb1b6ab..cb9e36d 100644
--- a/src/observability.ts
+++ b/src/observability.ts
@@ -1,4 +1,5 @@
 import { type Span, trace } from '@opentelemetry/api';
+import { redactSecrets } from './utils/secrets.js';
 
 type TelemetryMetadata = Record<string, unknown>;
 
@@ -84,7 +85,7 @@ function buildRootSpanAttributes(name: string, metadata: TelemetryMetadata): Rec
     attributes['langfuse.trace.tags'] = metadata.tags as string[];
   }
   if (metadata.input !== undefined) {
-    attributes['langfuse.trace.input'] = JSON.stringify(metadata.input);
+    attributes['langfuse.trace.input'] = redactSecrets(JSON.stringify(metadata.input));
   }
 
   return attributes;
diff --git a/src/utils/secrets.ts b/src/utils/secrets.ts
new file mode 100644
index 0000000..1ef1726
--- /dev/null
+++ b/src/utils/secrets.ts
@@ -0,0 +1,28 @@
+const MIN_SECRET_LENGTH = 4;
+const SECRET_NAME_TOKENS = ['password', 'passwd', 'secret', 'token', 'apikey', 'api_key', 'credential', 'private_key', 'privatekey', 'access_key'];
+const secretValues = new Set<string>();
+
+export function registerSecret(value: string): void {
+  if (!value) return;
+  if (value.length < MIN_SECRET_LENGTH) return;
+  secretValues.add(value);
+}
+
+export function redactSecrets(text: string): string {
+  if (!text) return text;
+  let result = text;
+  for (const value of [...secretValues].sort((a, b) => b.length - a.length)) {
+    if (!result.includes(value)) continue;
+    result = result.split(value).join('***REDACTED***');
+  }
+  return result;
+}
+
+export function clearRegisteredSecrets(): void {
+  secretValues.clear();
+}
+
+export function isSecretName(name: string): boolean {
+  const lower = name.toLowerCase();
+  return SECRET_NAME_TOKENS.some((token) => lower.includes(token));
+}
diff --git a/tests/unit/knowledge-tracker.test.ts b/tests/unit/knowledge-tracker.test.ts
index 6626096..7f46100 100644
--- a/tests/unit/knowledge-tracker.test.ts
+++ b/tests/unit/knowledge-tracker.test.ts
@@ -4,6 +4,7 @@ import { mkdirSync, writeFileSync } from 'node:fs';
 import matter from 'gray-matter';
 import { ConfigParser } from '../../src/config';
 import { KnowledgeTracker } from '../../src/knowledge-tracker';
+import { clearRegisteredSecrets, redactSecrets } from '../../src/utils/secrets';
 
 const knowledgeDir = '/tmp/explorbot-test-knowledge';
 
@@ -124,5 +125,32 @@ describe('KnowledgeTracker', () => {
       expect(content[0]).toContain('value:');
       expect(content[0]).not.toContain('${config.');
     });
+
+    it('should block credential-named config keys from interpolating', () => {
+      (ConfigParser.getInstance() as any).config.ai.apiKey = 'sk-should-not-leak';
+      writeKnowledgeFile('page.md', '/page', 'key: ${config.ai.apiKey}');
+
+      const tracker = new KnowledgeTracker();
+      const content = tracker.getKnowledgeForUrl('/page');
+
+      expect(content[0]).not.toContain('sk-should-not-leak');
+      expect(content[0]).not.toContain('${config.');
+    });
+
+    it('should register env secrets so they are redacted at sinks', () => {
+      clearRegisteredSecrets();
+      process.env.APP_PASSWORD = 'hunter2secret';
+
+      writeKnowledgeFile('login.md', '/login', 'password: ${env.APP_PASSWORD}');
+
+      const tracker = new KnowledgeTracker();
+      const content = tracker.getKnowledgeForUrl('/login');
+
+      expect(content[0]).toContain('password: hunter2secret');
+      expect(redactSecrets('typed hunter2secret into the field')).toBe('typed ***REDACTED*** into the field');
+
+      process.env.APP_PASSWORD = undefined;
+      clearRegisteredSecrets();
+    });
   });
 });
diff --git a/tests/unit/secrets.test.ts b/tests/unit/secrets.test.ts
new file mode 100644
index 0000000..0dc847b
--- /dev/null
+++ b/tests/unit/secrets.test.ts
@@ -0,0 +1,42 @@
+import { beforeEach, describe, expect, it } from 'bun:test';
+import { clearRegisteredSecrets, isSecretName, redactSecrets, registerSecret } from '../../src/utils/secrets';
+
+describe('secrets', () => {
+  beforeEach(() => {
+    clearRegisteredSecrets();
+  });
+
+  it('redacts a registered value', () => {
+    registerSecret('hunter2secret');
+    expect(redactSecrets('login with hunter2secret now')).toBe('login with ***REDACTED*** now');
+  });
+
+  it('passes unregistered values through unchanged', () => {
+    registerSecret('hunter2secret');
+    expect(redactSecrets('nothing to hide here')).toBe('nothing to hide here');
+  });
+
+  it('does not redact short values', () => {
+    registerSecret('12');
+    expect(redactSecrets('code 12 is fine')).toBe('code 12 is fine');
+  });
+
+  it('replaces every occurrence', () => {
+    registerSecret('topsecret');
+    expect(redactSecrets('topsecret and topsecret again')).toBe('***REDACTED*** and ***REDACTED*** again');
+  });
+
+  it('redacts a longer secret fully even when a registered secret is its substring', () => {
+    registerSecret('hunter2');
+    registerSecret('hunter2extended');
+    expect(redactSecrets('login with hunter2extended now')).toBe('login with ***REDACTED*** now');
+  });
+
+  it('detects credential-named keys', () => {
+    expect(isSecretName('APP_PASSWORD')).toBe(true);
+    expect(isSecretName('ai.apiKey')).toBe(true);
+    expect(isSecretName('SESSION_TOKEN')).toBe(true);
+    expect(isSecretName('BASE_URL')).toBe(false);
+    expect(isSecretName('playwright.browser')).toBe(false);
+  });
+});