diff --git a/server/src/nest-mcp/README.md b/server/src/nest-mcp/README.md
index f10535219..0bbf9bd1e 100644
--- a/server/src/nest-mcp/README.md
+++ b/server/src/nest-mcp/README.md
@@ -24,7 +24,7 @@ export class ThingsMcp {
   @Tool({
     name: 'list_things',
     description: 'List all things.',
-    inputSchema: {},                             // ZodRawShape, passed straight to the SDK
+    inputSchema: {},                             // ZodRawShape, registered as a strict object
     annotations: { readOnlyHint: true },
     access: { group: 'things', mode: 'read' },   // resolved by the accessPolicy
   })
@@ -34,7 +34,7 @@ export class ThingsMcp {
 }
 ```
 
-- `@Tool(options)` — mirrors `server.registerTool` (`name`, `title`, `description`, `inputSchema`, `outputSchema`, `annotations`, `_meta`). Handler: `(args, ctx)`; `args` is `{}` when no `inputSchema` was declared.
+- `@Tool(options)` — mirrors `server.registerTool` (`name`, `title`, `description`, `inputSchema`, `outputSchema`, `annotations`, `_meta`). Handler: `(args, ctx)`; `args` is `{}` when no `inputSchema` was declared. A shape is registered as `z.strictObject`, so an argument the tool never declared is refused (`Unrecognized key`) and `tools/list` advertises `additionalProperties: false`; the SDK's own wrapping would strip it and run the handler regardless. A whole Zod schema is passed through as written.
 - `@Resource(options)` — fixed URI (`uri`, `mimeType`, …). Handler: `(uri: URL, ctx)`.
 - `@ResourceTemplate(options)` — `uriTemplate` (RFC 6570). Handler: `(uri: URL, variables, ctx)`. (No `list`/`complete` template callbacks yet — extend when a domain needs them.)
 - `@Prompt(options)` — mirrors `registerPrompt` (`argsSchema` entries must be string-valued Zod schemas). Handler: `(args, ctx)`.
diff --git a/server/src/nest-mcp/registry.ts b/server/src/nest-mcp/registry.ts
index ab020875e..acfa565cd 100644
--- a/server/src/nest-mcp/registry.ts
+++ b/server/src/nest-mcp/registry.ts
@@ -15,12 +15,24 @@ import type {
 } from './types';
 import { ResourceTemplate as SdkResourceTemplate } from '@modelcontextprotocol/sdk/server/mcp';
 import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp';
+import { z } from 'zod';
 
 interface BoundEntry {
   entry: McpEntry;
   instance: object;
 }
 
+/**
+ * A shape is registered strict: the SDK's own z.object wrapping would strip an
+ * undeclared key and run the handler as if nothing was wrong, and strict also
+ * puts `additionalProperties: false` into tools/list. A whole schema is the
+ * author's call and passes through untouched.
+ */
+function strictInputSchema(schema: ToolOptions['inputSchema']): unknown {
+  if (schema === undefined || '_zod' in schema) return schema;
+  return z.strictObject(schema);
+}
+
 export interface McpRegistryOptions {
   accessPolicy?: McpAccessPolicy;
   validateAccess?: McpAccessValidator;
@@ -30,9 +42,9 @@ type AnyHandler = (this: unknown, ...handlerArgs: unknown[]) => unknown;
 
 /**
  * Structural view of the SDK registration surface. The SDK's real signatures
- * are generic over the Zod shapes; the registry passes schemas straight
- * through and binds `ctx` where the SDK would pass `extra`, so it needs (and
- * exposes) none of that type-level machinery.
+ * are generic over the Zod shapes; the registry hands schemas over as objects
+ * and binds `ctx` where the SDK would pass `extra`, so it needs (and exposes)
+ * none of that type-level machinery.
  */
 interface LooseRegistrar {
   registerTool(name: string, config: Record<string, unknown>, cb: (...cbArgs: unknown[]) => unknown): unknown;
@@ -294,7 +306,7 @@ export class McpRegistry {
     const config: Record<string, unknown> = {
       title: options.title,
       description: options.description,
-      inputSchema: options.inputSchema,
+      inputSchema: strictInputSchema(options.inputSchema),
       outputSchema: options.outputSchema,
       annotations: options.annotations,
       _meta: options._meta,
diff --git a/server/src/nest-mcp/types.ts b/server/src/nest-mcp/types.ts
index 82b895fa1..e8e19686e 100644
--- a/server/src/nest-mcp/types.ts
+++ b/server/src/nest-mcp/types.ts
@@ -126,8 +126,9 @@ export interface McpZodSchema {
 }
 
 /**
- * Mirrors the SDK's `registerTool` config. `inputSchema` is passed straight
- * through — the SDK does the parsing/validation.
+ * Mirrors the SDK's `registerTool` config. A shape `inputSchema` is registered
+ * as a strict object (see registry.ts); a whole schema is passed as written. The
+ * SDK does the parsing/validation either way.
  * `annotations`/`_meta` are kept structural so the package's public d.ts
  * never imports deep SDK subpaths.
  */
diff --git a/server/src/nest/budget/budget.mcp.ts b/server/src/nest/budget/budget.mcp.ts
index 5664e0c92..77df7e97b 100644
--- a/server/src/nest/budget/budget.mcp.ts
+++ b/server/src/nest/budget/budget.mcp.ts
@@ -25,13 +25,13 @@ const budgetAddonOn = addonGate(ADDON_IDS.BUDGET);
  * signed like the REST contract's (#2176): a negative payer is the recipient
  * of a refund recorded as a negative expense.
  */
-const payersSchema = z.array(z.object({
+const payersSchema = z.array(z.strictObject({
   user_id: z.number().int().positive(),
   amount: z.number(),
 })).describe('Who actually paid, and how much each paid, in the expense currency. Ask the user; do not guess.');
 
 /** Reusable Zod shape for an unequal split: what each participant owes. Signed, like the REST contract (#2176). */
-const splitMembersSchema = z.array(z.object({
+const splitMembersSchema = z.array(z.strictObject({
   user_id: z.number().int().positive(),
   amount: z.number(),
 })).describe('Unequal split: what each participant owes, in the expense currency. The amounts must add up to the expense total. Ask the user; do not guess.');
diff --git a/server/src/nest/journey/journey.mcp.ts b/server/src/nest/journey/journey.mcp.ts
index 57a1aa719..46ed01502 100644
--- a/server/src/nest/journey/journey.mcp.ts
+++ b/server/src/nest/journey/journey.mcp.ts
@@ -63,7 +63,7 @@ type EntryVisibility = z.infer<typeof ENTRY_VISIBILITY>;
  * only the half it has, which is what the entry editor does when a place was
  * all good or all bad. The service stores nothing when both come back empty.
  */
-const PROS_CONS = z.object({
+const PROS_CONS = z.strictObject({
   pros: z.array(z.string()).default([]),
   cons: z.array(z.string()).default([]),
 });
diff --git a/server/src/nest/maps/maps.mcp.ts b/server/src/nest/maps/maps.mcp.ts
index 156e1d441..9f6b0e7ec 100644
--- a/server/src/nest/maps/maps.mcp.ts
+++ b/server/src/nest/maps/maps.mcp.ts
@@ -95,7 +95,7 @@ export class MapsMcp {
         z.enum(POI_CATEGORY_KEYS),
         z.array(z.enum(POI_CATEGORY_KEYS)).min(1).max(MAX_POI_CATEGORIES),
       ]).describe('Which kind of place to look for. Pass several to cover them in one query rather than one request per kind'),
-      bbox: z.object({
+      bbox: z.strictObject({
         south: z.number().min(-90).max(90).describe('Southern edge, latitude'),
         west: z.number().min(-180).max(180).describe('Western edge, longitude'),
         north: z.number().min(-90).max(90).describe('Northern edge, latitude'),
diff --git a/server/src/nest/packing/packing.mcp.ts b/server/src/nest/packing/packing.mcp.ts
index 047bc2cf5..f4e04031d 100644
--- a/server/src/nest/packing/packing.mcp.ts
+++ b/server/src/nest/packing/packing.mcp.ts
@@ -511,7 +511,7 @@ export class PackingMcp {
     description: 'Import multiple packing items at once from a list. Optionally assign each to a bag (by name — created if missing), set its weight, or pre-check it.',
     inputSchema: {
       tripId: z.number().int().positive(),
-      items: z.array(z.object({
+      items: z.array(z.strictObject({
         name: z.string().min(1).max(200),
         category: z.string().optional(),
         quantity: z.number().int().positive().optional(),
diff --git a/server/src/nest/plugins/contributions/plugin-search.mcp.ts b/server/src/nest/plugins/contributions/plugin-search.mcp.ts
index 056e5f27f..1f7d77fbd 100644
--- a/server/src/nest/plugins/contributions/plugin-search.mcp.ts
+++ b/server/src/nest/plugins/contributions/plugin-search.mcp.ts
@@ -35,7 +35,7 @@ export class PluginSearchMcp {
     description: 'Search for a place in the search indexes installed plugins provide, which are the ones TREK does not ship itself. Use it alongside search_place, never instead of it: search_place is TREK\'s own index and OpenStreetMap, this is whatever else the instance owner installed, and only these results can carry a rating — open data has none, so a question like "the best rated hotel near here" can only be answered from this list. Results have the same shape search_place returns, plus a `rating` and the `pluginId` that found them. Returns an empty list when no plugin provides a search index, which is the normal case.',
     inputSchema: {
       query: z.string().min(1).max(MAX_QUERY).describe('Place name or address to search for'),
-      near: z.object({ lat: z.number(), lng: z.number() })
+      near: z.strictObject({ lat: z.number(), lng: z.number() })
         .optional()
         .describe('Centre the search on a coordinate. Pass it whenever the trip has a destination: a bare name like "Central Station" otherwise resolves wherever the provider guesses'),
       lang: z.string().max(20).optional().describe('BCP 47 language for the result names, e.g. "de" or "ja"'),
diff --git a/server/src/nest/reservations/reservations.mcp.ts b/server/src/nest/reservations/reservations.mcp.ts
index fba5bb671..8fb29e9f1 100644
--- a/server/src/nest/reservations/reservations.mcp.ts
+++ b/server/src/nest/reservations/reservations.mcp.ts
@@ -47,7 +47,7 @@ const urlField = reservationUrlSchema.max(2000).optional()
 type TransportType = typeof CREATABLE_TRANSPORT_TYPES[number];
 type BookingType = typeof BOOKING_TYPES[number];
 
-const endpointObjectSchema = z.object({
+const endpointObjectSchema = z.strictObject({
   role: z.enum(['from', 'to', 'stop']).describe('Endpoint role: "from" (origin), "to" (destination), or "stop" (intermediate)'),
   sequence: z.number().int().min(0).describe('Order within the route (0-based)'),
   name: z.string().min(1).describe('Location name (e.g. "Paris Gare de Lyon", "ZRH Terminal 2")'),
@@ -520,7 +520,7 @@ export class ReservationsMcp {
     description: 'Update the display order of reservations within a day.',
     inputSchema: {
       tripId: z.number().int().positive(),
-      positions: z.array(z.object({
+      positions: z.array(z.strictObject({
         id: z.number().int().positive(),
         day_plan_position: z.number().int().min(0),
       })).describe('Array of { id, day_plan_position } pairs'),
diff --git a/server/src/nest/roadtrip/roadtrip.mcp.ts b/server/src/nest/roadtrip/roadtrip.mcp.ts
index c584bbab6..33de03f00 100644
--- a/server/src/nest/roadtrip/roadtrip.mcp.ts
+++ b/server/src/nest/roadtrip/roadtrip.mcp.ts
@@ -89,14 +89,14 @@ export class RoadtripMcp {
     inputSchema: {
       tripId: z.number().int().positive(),
       dayId: z.number().int().positive(),
-      vias: z.array(z.object({
+      vias: z.array(z.strictObject({
         after_order_index: z.number().int().min(0).describe('Which stop of the day this via follows, counting from 0'),
         lat: z.number().min(-90).max(90),
         lng: z.number().min(-180).max(180),
       })).max(100).describe('In the order the drive passes through them'),
       replace_legs: z.array(z.number().int().min(0)).max(100).optional()
         .describe('Legs to clear before inserting, by the index of the stop they follow'),
-      track: z.object({
+      track: z.strictObject({
         place_id: z.number().int().positive().describe('The imported track this chain was fitted to, as its place id'),
         stray_km: z.number().min(0).max(40_000).nullable().optional()
           .describe('How far the fitted route still runs from the track at its worst point'),
@@ -139,7 +139,7 @@ export class RoadtripMcp {
     inputSchema: {
       tripId: z.number().int().positive(),
       dayId: z.number().int().positive(),
-      vias: z.array(z.object({
+      vias: z.array(z.strictObject({
         id: z.number().int().positive(),
         after_order_index: z.number().int().min(0).describe('Which stop of the day the via now follows, counting from 0'),
       })).max(500),
diff --git a/server/tests/unit/mcp/tools-places.test.ts b/server/tests/unit/mcp/tools-places.test.ts
index 85b88acb2..d48ac5d7a 100644
--- a/server/tests/unit/mcp/tools-places.test.ts
+++ b/server/tests/unit/mcp/tools-places.test.ts
@@ -247,6 +247,23 @@ describe('Tool: update_place', () => {
     });
   });
 
+  it('refuses a misspelt field instead of silently updating nothing', async () => {
+    // An assistant wrote stopType for stop_type; the call used to come back as a
+    // success with the place untouched, and the road trip never got its fuel stop.
+    const { user } = createUser(testDb);
+    const trip = createTrip(testDb, user.id);
+    const place = createPlace(testDb, trip.id, { name: 'Aral Bad Segeberg' });
+    await withHarness(user.id, async (h) => {
+      const refused = await h.client.callTool({ name: 'update_place', arguments: { tripId: trip.id, placeId: place.id, stopType: 'fuel' } });
+      expect(refused.isError).toBe(true);
+      expect((refused.content as Array<{ text: string }>)[0].text).toMatch(/Unrecognized key.*stopType/);
+      expect((testDb.prepare('SELECT stop_type FROM places WHERE id = ?').get(place.id) as { stop_type: string | null }).stop_type).toBeNull();
+      expect(broadcastMock).not.toHaveBeenCalled();
+      const fixed = parseToolResult(await h.client.callTool({ name: 'update_place', arguments: { tripId: trip.id, placeId: place.id, stop_type: 'fuel' } })) as any;
+      expect(fixed.place.stop_type).toBe('fuel');
+    });
+  });
+
   it('sets image_url on an existing place (#37)', async () => {
     const { user } = createUser(testDb);
     const trip = createTrip(testDb, user.id);
diff --git a/server/tests/unit/nest-mcp/attach.test.ts b/server/tests/unit/nest-mcp/attach.test.ts
index ba5e826e0..42fc8c4de 100644
--- a/server/tests/unit/nest-mcp/attach.test.ts
+++ b/server/tests/unit/nest-mcp/attach.test.ts
@@ -43,6 +43,13 @@ class FixtureMcp {
     return { content: [{ type: 'text', text: `wrote as ${ctx.userId}` }] };
   }
 
+  // A whole schema, the way a plugin's manifest-built tool arrives: its author
+  // decided how open it is, and the registry must not tighten it.
+  @Tool({ name: 'loose_tool', inputSchema: z.looseObject({ name: z.string() }) })
+  async looseTool(args: Record<string, unknown>, ctx: TestCtx) {
+    return { content: [{ type: 'text', text: JSON.stringify({ args, userId: ctx.userId }) }] };
+  }
+
   @Tool({ name: 'predicate_tool', access: (ctx: McpContext) => (ctx as TestCtx).allow === true })
   async predicateTool(args: Record<string, never>, ctx: TestCtx) {
     return { content: [{ type: 'text', text: JSON.stringify({ args, userId: ctx.userId }) }] };
@@ -150,7 +157,7 @@ describe('McpRegistry.attach', () => {
   it('registers everything for a ctx passing all access checks', async () => {
     harness = await createAttachHarness(buildRegistry(), { userId: 7, canRead: true, canWrite: true, allow: true });
     const tools = (await harness.client.listTools()).tools.map((t) => t.name).sort();
-    expect(tools).toEqual(['open_tool', 'predicate_tool', 'read_tool', 'write_tool']);
+    expect(tools).toEqual(['loose_tool', 'open_tool', 'predicate_tool', 'read_tool', 'write_tool']);
     const resources = (await harness.client.listResources()).resources.map((r) => r.name);
     expect(resources).toEqual(['fixture_doc']);
     const templates = (await harness.client.listResourceTemplates()).resourceTemplates.map((t) => t.name);
@@ -162,13 +169,13 @@ describe('McpRegistry.attach', () => {
   it('filters declarative access through the policy per mode', async () => {
     harness = await createAttachHarness(buildRegistry(), { userId: 7, canRead: true, canWrite: false, allow: false });
     const tools = (await harness.client.listTools()).tools.map((t) => t.name).sort();
-    expect(tools).toEqual(['open_tool', 'read_tool']);
+    expect(tools).toEqual(['loose_tool', 'open_tool', 'read_tool']);
   });
 
   it('filters everything gated when the ctx grants nothing, keeping ungated entries', async () => {
     harness = await createAttachHarness(buildRegistry(), { userId: 7 });
     const tools = (await harness.client.listTools()).tools.map((t) => t.name).sort();
-    expect(tools).toEqual(['open_tool']);
+    expect(tools).toEqual(['loose_tool', 'open_tool']);
     expect((await harness.client.listResources()).resources).toEqual([]);
     const templates = (await harness.client.listResourceTemplates()).resourceTemplates.map((t) => t.name);
     expect(templates).toEqual(['fixture_item']);
@@ -188,6 +195,32 @@ describe('McpRegistry.attach', () => {
     expect(JSON.parse(textOf(result))).toEqual({ greeting: 'hello trek', userId: 42 });
   });
 
+  it('refuses an argument the tool never declared instead of stripping it', async () => {
+    harness = await createAttachHarness(buildRegistry(), { userId: 42, canRead: true, canWrite: true, allow: true });
+    // A shape is registered strict: the SDK would otherwise drop `nmae` and run
+    // the handler as if the caller had sent nothing wrong.
+    const refused = await harness.client.callTool({ name: 'read_tool', arguments: { name: 'trek', nmae: 'typo' } });
+    expect(refused.isError).toBe(true);
+    expect(textOf(refused)).toMatch(/Unrecognized key.*nmae/);
+    // An empty shape is strict too: nothing declared means nothing accepted.
+    const stray = await harness.client.callTool({ name: 'write_tool', arguments: { anything: 1 } });
+    expect(stray.isError).toBe(true);
+    expect(textOf(stray)).toMatch(/Unrecognized key.*anything/);
+    expect(textOf(await harness.client.callTool({ name: 'write_tool', arguments: {} }))).toBe('wrote as 42');
+    // tools/list says so up front, so a client that reads the schema never sends it.
+    const tools = (await harness.client.listTools()).tools;
+    expect(tools.find((t) => t.name === 'read_tool')?.inputSchema).toMatchObject({ additionalProperties: false });
+    expect(tools.find((t) => t.name === 'write_tool')?.inputSchema).toMatchObject({ additionalProperties: false });
+  });
+
+  it('hands a whole schema to the SDK as written, however open its author left it', async () => {
+    harness = await createAttachHarness(buildRegistry(), { userId: 42 });
+    const result = await harness.client.callTool({ name: 'loose_tool', arguments: { name: 'trek', extra: 'kept' } });
+    expect(JSON.parse(textOf(result))).toEqual({ args: { name: 'trek', extra: 'kept' }, userId: 42 });
+    const loose = (await harness.client.listTools()).tools.find((t) => t.name === 'loose_tool');
+    expect(loose?.inputSchema).not.toHaveProperty('additionalProperties', false);
+  });
+
   it('normalizes args to {} for tools declared without an inputSchema', async () => {
     harness = await createAttachHarness(buildRegistry(), { userId: 42 });
     const result = await harness.client.callTool({ name: 'open_tool', arguments: {} });
diff --git a/wiki/MCP-Tools-and-Resources.md b/wiki/MCP-Tools-and-Resources.md
index 7edcf4acf..63a27d60a 100644
--- a/wiki/MCP-Tools-and-Resources.md
+++ b/wiki/MCP-Tools-and-Resources.md
@@ -2,6 +2,8 @@
 
 TREK exposes **tools** (read and write actions) and **resources** (read-only `trek://` URIs). Tools are registered per-session based on OAuth scopes and enabled addons.
 
+Every built-in tool checks its arguments against its published schema before anything runs. An argument the tool does not declare (a misspelt field such as `stopType` for `stop_type`) is refused with `Unrecognized key`, so the AI sees the mistake and can retry rather than reporting a change that never happened. Plugin-contributed tools follow the schema their manifest declares.
+
 For addon-gated tools (Packing, To-Dos, Atlas, Collab, Collections, Vacay, Journey, Dawarich, Document sync, Road trip) and their resources, see [MCP-Addon-Tools](MCP-Addon-Tools).
 
 ## Tools