diff --git a/README.md b/README.md
index f4f030d..2f5d9f5 100644
--- a/README.md
+++ b/README.md
@@ -300,7 +300,7 @@ The metrics server only starts in HTTP mode (not stdio) and binds to `0.0.0.0` 
 
 - **`get_row_activities`** — Get change history of a row (who changed what, when, old/new values)
 - **`create_snapshot`** — Create a snapshot of the current base (10 min cooldown)
-- **`add_select_options`** — Add new options to single-select or multi-select columns
+- **`add_select_options`** — Add new options to single-select or multi-select columns (existing options are skipped, no duplicates)
 - **`ping_seatable`** — Health check with latency monitoring
 
 ## Supported Column Types
diff --git a/package.json b/package.json
index 513d3c5..aa3fa84 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@seatable/mcp-seatable",
-  "version": "1.6.1",
+  "version": "1.6.2",
   "type": "module",
   "license": "MIT",
   "mcpName": "io.github.seatable/seatable",
diff --git a/src/mcp/tools/addSelectOption.ts b/src/mcp/tools/addSelectOption.ts
index 14a46f2..68d0a29 100644
--- a/src/mcp/tools/addSelectOption.ts
+++ b/src/mcp/tools/addSelectOption.ts
@@ -1,5 +1,6 @@
 import { z } from 'zod'
 
+import { makeError } from '../../errors.js'
 import { ToolRegistrar } from './types.js'
 
 const InputSchema = z.object({
@@ -12,25 +13,67 @@ const InputSchema = z.object({
   })).min(1).describe('Array of options to add'),
 })
 
+/** Names of the options a select column already has. Empty if the column has none yet. */
+function existingOptionNames(metadata: any, table: string, column: string): Set<string> {
+  const tableObj = (metadata?.tables ?? []).find((t: any) => t.name === table)
+  if (!tableObj) {
+    throw makeError('ERR_SCHEMA_UNKNOWN_TABLE', `Table "${table}" not found`, { table })
+  }
+  const columnObj = (tableObj.columns ?? []).find((c: any) => c.name === column)
+  if (!columnObj) {
+    throw makeError('ERR_SCHEMA_UNKNOWN_COLUMN', `Column "${column}" not found in table "${table}"`, {
+      table,
+      column,
+    })
+  }
+  const opts = columnObj.data?.options
+  if (!Array.isArray(opts)) return new Set()
+  return new Set(
+    opts.map((o: any) => o?.name).filter((n: unknown): n is string => typeof n === 'string')
+  )
+}
+
 export const registerAddSelectOptions: ToolRegistrar = (server, { client, getInputSchema }) => {
   server.registerTool(
     'add_select_options',
     {
       title: 'Add Select Options',
-      description: 'Add new options to a single-select or multi-select column. Use this before writing rows with option values that do not exist yet.',
+      description: 'Add new options to a single-select or multi-select column. Use this before writing rows with option values that do not exist yet. Options that already exist are skipped, so this will not create duplicates.',
       inputSchema: getInputSchema(InputSchema),
       annotations: { readOnlyHint: false, destructiveHint: false, idempotentHint: true, openWorldHint: false },
     },
     async (args: unknown) => {
       const parsed = InputSchema.parse(args)
 
+      // Skip options the column already has — the SeaTable API happily creates
+      // a second option with the same name, which is never what the caller wants.
+      const existing = existingOptionNames(await client.getMetadata(), parsed.table, parsed.column)
+      const skipped: string[] = []
+      const seen = new Set<string>()
+      const toAdd: typeof parsed.options = []
+      for (const opt of parsed.options) {
+        if (existing.has(opt.name)) {
+          skipped.push(opt.name)
+        } else if (!seen.has(opt.name)) {
+          seen.add(opt.name)
+          toAdd.push(opt)
+        }
+      }
+
+      const added = toAdd.map((o) => o.name)
+      if (toAdd.length === 0) {
+        return {
+          content: [{ type: 'text', text: JSON.stringify({ added, skipped, success: true }) }],
+        }
+      }
+
       const result = await client.addColumnOptions({
         table: parsed.table,
         column: parsed.column,
-        options: parsed.options,
+        options: toAdd,
       })
 
-      return { content: [{ type: 'text', text: JSON.stringify(result) }] }
+      return { content: [{ type: 'text', text: JSON.stringify({ added, skipped, ...result }) }] }
     }
   )
 }
diff --git a/src/schema/validate.ts b/src/schema/validate.ts
index 0eebb71..2a58d36 100644
--- a/src/schema/validate.ts
+++ b/src/schema/validate.ts
@@ -132,9 +132,14 @@ function validateDate(colName: string, value: unknown): void {
 }
 
 function getSelectOptions(col: GenericColumn): Set<string> {
-    const opts = col.options?.options as Array<{ name: string }> | undefined
+    // Options arrive in two shapes: the raw SeaTable form ([{ name, id, color }])
+    // and the flattened form produced by mapMetadataToGeneric (["open", "closed"]).
+    const opts = col.options?.options as Array<{ name?: unknown } | string> | undefined
     if (!Array.isArray(opts)) return new Set()
-    return new Set(opts.map((o) => o.name))
+    const names = opts
+        .map((o) => (typeof o === 'string' ? o : (o as { name?: unknown })?.name))
+        .filter((n): n is string => typeof n === 'string' && n !== '')
+    return new Set(names)
 }
 
 function validateSingleSelect(colName: string, value: unknown, col: GenericColumn): void {
diff --git a/tests/addSelectOptions.spec.ts b/tests/addSelectOptions.spec.ts
new file mode 100644
index 0000000..2ee39f9
--- /dev/null
+++ b/tests/addSelectOptions.spec.ts
@@ -0,0 +1,131 @@
+import { describe, expect, it } from 'vitest'
+
+import { registerAddSelectOptions } from '../src/mcp/tools/addSelectOption.js'
+import type { ClientLike } from '../src/mcp/tools/types.js'
+
+type Handler = (args: unknown) => Promise<any>
+
+/** Metadata with one single-select column that already has two options. */
+function metadataWithOptions(names: string[]) {
+    return {
+        tables: [
+            {
+                _id: 'tbl1',
+                name: 'Tasks',
+                columns: [
+                    { key: 'col1', name: 'Title', type: 'text' },
+                    {
+                        key: 'col2',
+                        name: 'Statut',
+                        type: 'single-select',
+                        data: { options: names.map((n, i) => ({ id: `o${i}`, name: n, color: '#fff' })) },
+                    },
+                ],
+            },
+        ],
+    }
+}
+
+/** Wire the registrar to a fake client and return the handler plus recorded calls. */
+function setup(existing: string[]) {
+    const calls: Array<{ table: string; column: string; options: Array<{ name: string }> }> = []
+    const client = {
+        getMetadata: async () => metadataWithOptions(existing),
+        addColumnOptions: async (args: any) => {
+            calls.push(args)
+            return { success: true }
+        },
+    } as unknown as ClientLike
+
+    let handler: Handler | undefined
+    const server = {
+        registerTool: (_name: string, _cfg: unknown, h: Handler) => {
+            handler = h
+        },
+    }
+
+    registerAddSelectOptions(server as any, {
+        client,
+        env: {} as any,
+        getInputSchema: (s: any) => s,
+    })
+
+    return { handler: handler as Handler, calls }
+}
+
+function parse(result: any): any {
+    return JSON.parse(result.content[0].text)
+}
+
+describe('add_select_options', () => {
+    it('adds options that do not exist yet', async () => {
+        const { handler, calls } = setup(['En cours'])
+        const result = await handler({
+            table: 'Tasks',
+            column: 'Statut',
+            options: [{ name: 'Reconnu' }],
+        })
+
+        expect(calls).toHaveLength(1)
+        expect(calls[0].options.map((o) => o.name)).toEqual(['Reconnu'])
+        expect(parse(result).added).toEqual(['Reconnu'])
+    })
+
+    it('skips options that already exist instead of duplicating them', async () => {
+        const { handler, calls } = setup(['En cours', 'Reconnu'])
+        const result = await handler({
+            table: 'Tasks',
+            column: 'Statut',
+            options: [{ name: 'En cours' }, { name: 'Non reconnu' }],
+        })
+
+        expect(calls).toHaveLength(1)
+        expect(calls[0].options.map((o) => o.name)).toEqual(['Non reconnu'])
+        const data = parse(result)
+        expect(data.added).toEqual(['Non reconnu'])
+        expect(data.skipped).toEqual(['En cours'])
+    })
+
+    it('makes no API call when every option already exists', async () => {
+        const { handler, calls } = setup(['En cours', 'Reconnu'])
+        const result = await handler({
+            table: 'Tasks',
+            column: 'Statut',
+            options: [{ name: 'En cours' }, { name: 'Reconnu' }],
+        })
+
+        expect(calls).toHaveLength(0)
+        const data = parse(result)
+        expect(data.added).toEqual([])
+        expect(data.skipped).toEqual(['En cours', 'Reconnu'])
+    })
+
+    it('collapses duplicates within a single request', async () => {
+        const { handler, calls } = setup([])
+        await handler({
+            table: 'Tasks',
+            column: 'Statut',
+            options: [{ name: 'Nouveau' }, { name: 'Nouveau' }],
+        })
+
+        expect(calls[0].options.map((o) => o.name)).toEqual(['Nouveau'])
+    })
+
+    it('treats option names as case-sensitive, like SeaTable does', async () => {
+        const { handler, calls } = setup(['En cours'])
+        await handler({
+            table: 'Tasks',
+            column: 'Statut',
+            options: [{ name: 'EN COURS' }],
+        })
+
+        expect(calls[0].options.map((o) => o.name)).toEqual(['EN COURS'])
+    })
+
+    it('fails clearly when the column does not exist', async () => {
+        const { handler } = setup(['En cours'])
+        await expect(
+            handler({ table: 'Tasks', column: 'Nope', options: [{ name: 'x' }] })
+        ).rejects.toThrow(/Nope/)
+    })
+})
diff --git a/tests/validate.spec.ts b/tests/validate.spec.ts
index 94083ed..5689d85 100644
--- a/tests/validate.spec.ts
+++ b/tests/validate.spec.ts
@@ -311,3 +311,41 @@ describe('validateRowsAgainstSchema', () => {
     })
   })
 })
+
+// Regression: the shape produced by mapMetadataToGeneric must validate correctly.
+// mapMetadataToGeneric flattens select options to a string array ({ options: ['open'] }),
+// while the fixtures above use the raw SeaTable object form ({ options: [{ name: 'open' }] }).
+// Both must be accepted — see ticket "unknown option ... Valid options: <empty>".
+describe('select validation against mapped schema shape', () => {
+  const mappedSchema: GenericSchema = {
+    base_id: 'base1',
+    tables: [
+      {
+        id: 'tbl1',
+        name: 'Tasks',
+        columns: [
+          { id: 'col1', name: 'Title', type: 'text' },
+          { id: 'col2', name: 'Statut', type: 'single_select', options: { options: ['En cours', 'Reconnu'] } },
+          { id: 'col3', name: 'Tags', type: 'multi_select', options: { options: ['urgent', 'low'] } },
+        ],
+      },
+    ],
+  }
+
+  it('accepts a valid single-select option', () => {
+    const rows = [{ Title: 'A', Statut: 'En cours' }]
+    validateRowsAgainstSchema(mappedSchema, 'Tasks', rows)
+  })
+
+  it('accepts valid multi-select options', () => {
+    const rows = [{ Title: 'A', Tags: ['urgent'] }]
+    validateRowsAgainstSchema(mappedSchema, 'Tasks', rows)
+  })
+
+  it('still rejects an unknown option and lists the valid ones', () => {
+    const rows = [{ Title: 'A', Statut: 'Nope' }]
+    expect(() => validateRowsAgainstSchema(mappedSchema, 'Tasks', rows)).toThrowError(
+      'unknown option "Nope". Valid options: En cours, Reconnu'
+    )
+  })
+})