diff --git a/integration-tests/cron-tools.test.ts b/integration-tests/cron-tools.test.ts
index 6a69ffa30..485eec1f2 100644
--- a/integration-tests/cron-tools.test.ts
+++ b/integration-tests/cron-tools.test.ts
@@ -65,7 +65,7 @@ describe('cron-tools', () => {
     });
 
     const result = await rig.run(
-      'Call cron_create with cron_expression "*/5 * * * *", prompt "test ping", recurring true. Then call cron_list. Then delete that job using cron_delete. Then call cron_list again. How many jobs remain? Reply with just the number.',
+      'Call cron_create with cron "*/5 * * * *", prompt "test ping", recurring true. Then call cron_list. Then delete that job using cron_delete. Then call cron_list again. How many jobs remain? Reply with just the number.',
     );
 
     const foundCreate = await rig.waitForToolCall('cron_create');
@@ -94,7 +94,7 @@ describe('cron-tools', () => {
     });
 
     const result = await rig.run(
-      'Do these steps: (1) Call cron_create with cron_expression "*/5 * * * *", prompt "one-shot test", recurring false. (2) Call cron_list. Is the job marked as recurring or one-shot? Remember the answer. (3) Delete all cron jobs. Reply with just "recurring" or "one-shot".',
+      'Do these steps: (1) Call cron_create with cron "*/5 * * * *", prompt "one-shot test", recurring false. (2) Call cron_list. Is the job marked as recurring or one-shot? Remember the answer. (3) Delete all cron jobs. Reply with just "recurring" or "one-shot".',
     );
 
     const foundCreate = await rig.waitForToolCall('cron_create');
diff --git a/packages/core/src/skills/bundled/loop/SKILL.md b/packages/core/src/skills/bundled/loop/SKILL.md
index 0b0969eca..074ff02ae 100644
--- a/packages/core/src/skills/bundled/loop/SKILL.md
+++ b/packages/core/src/skills/bundled/loop/SKILL.md
@@ -29,7 +29,7 @@ You are setting up a recurring in-session loop. Parse the user's input to extrac
 2. Convert the interval to a cron expression
 3. Append to the prompt: `\n\nBe concise. If nothing has changed, reply with a single short sentence.`
 4. Call `cron_create` with:
-   - `cron_expression`: the computed cron expression
+   - `cron`: the computed cron expression
    - `prompt`: the extracted prompt with the conciseness instruction appended
    - `recurring`: true
 5. Confirm to the user: "Loop created — I'll [description] every [interval]."
diff --git a/packages/core/src/tools/cron-create.test.ts b/packages/core/src/tools/cron-create.test.ts
index a44eae733..74145f424 100644
--- a/packages/core/src/tools/cron-create.test.ts
+++ b/packages/core/src/tools/cron-create.test.ts
@@ -27,7 +27,7 @@ describe('CronCreateTool', () => {
 
   it('creates a recurring job by default', async () => {
     const invocation = tool.build({
-      cron_expression: '*/5 * * * *',
+      cron: '*/5 * * * *',
       prompt: 'check status',
     });
     const result = await invocation.execute(new AbortController().signal);
@@ -39,7 +39,7 @@ describe('CronCreateTool', () => {
 
   it('creates a one-shot job when recurring=false', async () => {
     const invocation = tool.build({
-      cron_expression: '*/1 * * * *',
+      cron: '*/1 * * * *',
       prompt: 'once',
       recurring: false,
     });
@@ -53,7 +53,7 @@ describe('CronCreateTool', () => {
 
   it('returns error for invalid cron expression', async () => {
     const invocation = tool.build({
-      cron_expression: 'bad cron',
+      cron: 'bad cron',
       prompt: 'fail',
     });
     const result = await invocation.execute(new AbortController().signal);
@@ -61,9 +61,7 @@ describe('CronCreateTool', () => {
   });
 
   it('validates required params', () => {
-    expect(() =>
-      tool.build({ cron_expression: '*/1 * * * *' } as never),
-    ).toThrow();
+    expect(() => tool.build({ cron: '*/1 * * * *' } as never)).toThrow();
     expect(() => tool.build({ prompt: 'test' } as never)).toThrow();
   });
 });
diff --git a/packages/core/src/tools/cron-create.ts b/packages/core/src/tools/cron-create.ts
index cdfaba286..94edff3b3 100644
--- a/packages/core/src/tools/cron-create.ts
+++ b/packages/core/src/tools/cron-create.ts
@@ -9,7 +9,7 @@ import type { Config } from '../config/config.js';
 import { nextFireTime } from '../utils/cronParser.js';
 
 export interface CronCreateParams {
-  cron_expression: string;
+  cron: string;
   prompt: string;
   recurring?: boolean;
 }
@@ -28,7 +28,7 @@ class CronCreateInvocation extends BaseToolInvocation<
   getDescription(): string {
     const recurrence =
       this.params.recurring !== false ? 'recurring' : 'one-shot';
-    return `Create ${recurrence} cron job: ${this.params.cron_expression}`;
+    return `Create ${recurrence} cron job: ${this.params.cron}`;
   }
 
   async execute(): Promise<ToolResult> {
@@ -37,12 +37,12 @@ class CronCreateInvocation extends BaseToolInvocation<
 
     try {
       const job = scheduler.create(
-        this.params.cron_expression,
+        this.params.cron,
         this.params.prompt,
         recurring,
       );
 
-      const next = nextFireTime(this.params.cron_expression, new Date());
+      const next = nextFireTime(this.params.cron, new Date());
       const result = [
         `Created ${recurring ? 'recurring' : 'one-shot'} cron job.`,
         `  ID: ${job.id}`,
@@ -76,34 +76,49 @@ export class CronCreateTool extends BaseDeclarativeTool<
     super(
       CronCreateTool.Name,
       ToolDisplayNames.CRON_CREATE,
-      'Create a new in-session cron job that fires a prompt on a schedule. ' +
-        'The job runs within the current session and is gone when the session ends. ' +
-        'Use standard 5-field cron expressions (minute hour day-of-month month day-of-week). ' +
-        'Examples: "*/5 * * * *" (every 5 min), "0 */2 * * *" (every 2 hours), "*/1 * * * *" (every minute).',
+      'Schedule a prompt to be enqueued at a future time. Use for both recurring schedules and one-shot reminders.\n\n' +
+        'Uses standard 5-field cron in the user\'s local timezone: minute hour day-of-month month day-of-week. "0 9 * * *" means 9am local — no timezone conversion needed.\n\n' +
+        '## One-shot tasks (recurring: false)\n\n' +
+        'For "remind me at X" or "at <time>, do Y" requests — fire once then auto-delete.\n' +
+        'Pin minute/hour/day-of-month/month to specific values:\n' +
+        '  "remind me at 2:30pm today to check the deploy" → cron: "30 14 <today_dom> <today_month> *", recurring: false\n' +
+        '  "tomorrow morning, run the smoke test" → cron: "57 8 <tomorrow_dom> <tomorrow_month> *", recurring: false\n\n' +
+        '## Recurring jobs (recurring: true, the default)\n\n' +
+        'For "every N minutes" / "every hour" / "weekdays at 9am" requests:\n' +
+        '  "*/5 * * * *" (every 5 min), "0 * * * *" (hourly), "0 9 * * 1-5" (weekdays at 9am local)\n\n' +
+        '## Avoid the :00 and :30 minute marks when the task allows it\n\n' +
+        'Every user who asks for "9am" gets `0 9`, and every user who asks for "hourly" gets `0 *` — which means requests from across the planet land on the API at the same instant. When the user\'s request is approximate, pick a minute that is NOT 0 or 30:\n' +
+        '  "every morning around 9" → "57 8 * * *" or "3 9 * * *" (not "0 9 * * *")\n' +
+        '  "hourly" → "7 * * * *" (not "0 * * * *")\n' +
+        '  "in an hour or so, remind me to..." → pick whatever minute you land on, don\'t round\n\n' +
+        'Only use minute 0 or 30 when the user names that exact time and clearly means it ("at 9:00 sharp", "at half past", coordinating with a meeting). When in doubt, nudge a few minutes early or late — the user will not notice, and the fleet will.\n\n' +
+        '## Session-only\n\n' +
+        'Jobs live only in this Claude session — nothing is written to disk, and the job is gone when Claude exits.\n\n' +
+        '## Runtime behavior\n\n' +
+        'Jobs only fire while the REPL is idle (not mid-query). The scheduler adds a small deterministic jitter on top of whatever you pick: recurring tasks fire up to 10% of their period late (max 15 min); one-shot tasks landing on :00 or :30 fire up to 90 s early. Picking an off-minute is still the bigger lever.\n\n' +
+        'Recurring tasks auto-expire after 3 days — they fire one final time, then are deleted. This bounds session lifetime. Tell the user about the 3-day limit when scheduling recurring jobs.\n\n' +
+        'Returns a job ID you can pass to CronDelete.',
       Kind.Other,
       {
         type: 'object',
         properties: {
-          cron_expression: {
+          cron: {
             type: 'string',
             description:
-              'Standard 5-field cron expression. Fields: minute (0-59), hour (0-23), ' +
-              'day-of-month (1-31), month (1-12), day-of-week (0-6, 0=Sunday). ' +
-              'Supports: *, values, ranges (1-5), steps (*/15), lists (1,15,30).',
+              'Standard 5-field cron expression in local time: "M H DoM Mon DoW" (e.g. "*/5 * * * *" = every 5 minutes, "30 14 28 2 *" = Feb 28 at 2:30pm local once).',
           },
           prompt: {
             type: 'string',
-            description:
-              'The prompt to send when the job fires. This is injected into the ' +
-              'session as if the user typed it.',
+            description: 'The prompt to enqueue at each fire time.',
           },
           recurring: {
             type: 'boolean',
             description:
-              'If true (default), the job fires repeatedly. If false, it fires once and is deleted.',
+              'true (default) = fire on every cron match until deleted or auto-expired after 3 days. false = fire once at the next match, then auto-delete. Use false for "remind me at X" one-shot requests with pinned minute/hour/dom/month.',
           },
         },
-        required: ['cron_expression', 'prompt'],
+        required: ['cron', 'prompt'],
+        additionalProperties: false,
       },
     );
   }
diff --git a/packages/core/src/tools/cron-delete.ts b/packages/core/src/tools/cron-delete.ts
index 487c69939..799fc476a 100644
--- a/packages/core/src/tools/cron-delete.ts
+++ b/packages/core/src/tools/cron-delete.ts
@@ -54,17 +54,18 @@ export class CronDeleteTool extends BaseDeclarativeTool<
     super(
       CronDeleteTool.Name,
       ToolDisplayNames.CRON_DELETE,
-      'Delete an active in-session cron job by its ID. Use cron_list to find job IDs.',
+      'Cancel a cron job previously scheduled with CronCreate. Removes it from the in-memory session store.',
       Kind.Other,
       {
         type: 'object',
         properties: {
           id: {
             type: 'string',
-            description: 'The 8-character ID of the cron job to delete.',
+            description: 'Job ID returned by CronCreate.',
           },
         },
         required: ['id'],
+        additionalProperties: false,
       },
     );
   }
diff --git a/packages/core/src/tools/cron-list.ts b/packages/core/src/tools/cron-list.ts
index b128938a1..b3e616e57 100644
--- a/packages/core/src/tools/cron-list.ts
+++ b/packages/core/src/tools/cron-list.ts
@@ -68,11 +68,12 @@ export class CronListTool extends BaseDeclarativeTool<
     super(
       CronListTool.Name,
       ToolDisplayNames.CRON_LIST,
-      'List all active in-session cron jobs, including their IDs, schedules, and next fire times.',
+      'List all cron jobs scheduled via CronCreate in this session.',
       Kind.Other,
       {
         type: 'object',
         properties: {},
+        additionalProperties: false,
       },
     );
   }