diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 1f623e3..571d369 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -23,8 +23,8 @@ jobs:
           node-version-file: .nvmrc
           cache: "pnpm"
       - run: pnpm install
+      - run: pnpm build
       - uses: reviewdog/action-eslint@v1.32.0
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           reporter: github-pr-review # Change reporter.
-      - run: pnpm build
diff --git a/packages/integration-tests/cypress/e2e/neovim.cy.ts b/packages/integration-tests/cypress/e2e/neovim.cy.ts
index f92a5dd..211621d 100644
--- a/packages/integration-tests/cypress/e2e/neovim.cy.ts
+++ b/packages/integration-tests/cypress/e2e/neovim.cy.ts
@@ -120,4 +120,55 @@ describe("neovim features", () => {
       })
     })
   })
+
+  it("can run lua code and get its result", () => {
+    cy.visit("/")
+    cy.startNeovim().then(() => {
+      // wait until text on the start screen is visible
+      cy.contains("If you see this text, Neovim is ready!")
+
+      // can do math
+      cy.runLuaCode({ luaCode: "return 40 + 2" }).then(result => {
+        expect(result.value).to.equal(42)
+      })
+
+      // can return strings
+      cy.runLuaCode({ luaCode: "return 'hello from lua'" }).then(result => {
+        expect(result.value).to.equal("hello from lua")
+      })
+
+      // can use nvim apis
+      cy.runLuaCode({ luaCode: "return vim.api.nvim_get_current_win()" }).then(result => {
+        expect(result.value).to.equal(1000)
+      })
+
+      // does not return anything if the lua code does not return anything.
+      // But side effects are visible in the neovim instance.
+      cy.runLuaCode({ luaCode: `vim.api.nvim_command('echo "hello from lua"')` }).then(result => {
+        expect(result.value).to.equal(null)
+      })
+      cy.contains("hello from lua")
+
+      // can programmatically manipulate the buffer
+      cy.runLuaCode({
+        luaCode: `
+        vim.api.nvim_buf_set_lines(0, 0, -1, false, {'hello', 'from', 'lua'})
+      `,
+      })
+      cy.contains("If you see this text, Neovim is ready!").should("not.exist")
+      cy.contains("hello")
+      cy.contains("from")
+      cy.contains("lua")
+
+      // can return tables
+      cy.runLuaCode({ luaCode: "return {1, 2, 3}" }).then(result => {
+        expect(result.value).to.deep.equal([1, 2, 3])
+      })
+
+      // can return nested tables
+      cy.runLuaCode({ luaCode: "return {1, {2, 3}, 4}" }).then(result => {
+        expect(result.value).to.deep.equal([1, [2, 3], 4])
+      })
+    })
+  })
 })
diff --git a/packages/integration-tests/cypress/support/tui-sandbox.ts b/packages/integration-tests/cypress/support/tui-sandbox.ts
index 3f285bd..a638332 100644
--- a/packages/integration-tests/cypress/support/tui-sandbox.ts
+++ b/packages/integration-tests/cypress/support/tui-sandbox.ts
@@ -2,9 +2,10 @@
 //
 // This file is autogenerated by tui-sandbox. Do not edit it directly.
 //
-import type { BlockingCommandClientInput } from "@tui-sandbox/library/dist/src/server/server"
+import type { BlockingCommandClientInput, LuaCodeClientInput } from "@tui-sandbox/library/dist/src/server/server"
 import type {
   BlockingShellCommandOutput,
+  RunLuaCodeOutput,
   StartNeovimGenericArguments,
 } from "@tui-sandbox/library/dist/src/server/types"
 import type { OverrideProperties } from "type-fest"
@@ -19,6 +20,7 @@ declare global {
   interface Window {
     startNeovim(startArguments?: MyStartNeovimServerArguments): Promise<NeovimContext>
     runBlockingShellCommand(input: BlockingCommandClientInput): Promise<BlockingShellCommandOutput>
+    runLuaCode(input: LuaCodeClientInput): Promise<RunLuaCodeOutput>
   }
 }
 
@@ -49,6 +51,12 @@ Cypress.Commands.add("typeIntoTerminal", (text: string, options?: Partial<Cypres
   cy.get("textarea").focus().type(text, options)
 })
 
+Cypress.Commands.add("runLuaCode", (input: LuaCodeClientInput) => {
+  cy.window().then(async win => {
+    return await win.runLuaCode(input)
+  })
+})
+
 before(function () {
   // disable Cypress's default behavior of logging all XMLHttpRequests and
   // fetches to the Command Log
@@ -68,6 +76,8 @@ declare global {
       /** Runs a shell command in a blocking manner, waiting for the command to
        * finish before returning. Requires neovim to be running. */
       runBlockingShellCommand(input: BlockingCommandClientInput): Chainable<BlockingShellCommandOutput>
+
+      runLuaCode(input: LuaCodeClientInput): Chainable<RunLuaCodeOutput>
     }
   }
 }
diff --git a/packages/library/src/browser/neovim-client.ts b/packages/library/src/browser/neovim-client.ts
index 69920a8..97e3278 100644
--- a/packages/library/src/browser/neovim-client.ts
+++ b/packages/library/src/browser/neovim-client.ts
@@ -1,6 +1,11 @@
 import { TerminalClient } from "../client/index.js"
-import type { BlockingCommandClientInput } from "../server/server.js"
-import type { BlockingShellCommandOutput, StartNeovimGenericArguments, TestDirectory } from "../server/types.js"
+import type { BlockingCommandClientInput, LuaCodeClientInput } from "../server/server.js"
+import type {
+  BlockingShellCommandOutput,
+  RunLuaCodeOutput,
+  StartNeovimGenericArguments,
+  TestDirectory,
+} from "../server/types.js"
 
 const app = document.querySelector<HTMLElement>("#app")
 if (!app) {
@@ -26,9 +31,14 @@ window.runBlockingShellCommand = async function (
   return client.runBlockingShellCommand(input)
 }
 
+window.runLuaCode = async function (input: LuaCodeClientInput): Promise<RunLuaCodeOutput> {
+  return client.runLuaCode(input)
+}
+
 declare global {
   interface Window {
     startNeovim(startArguments?: StartNeovimGenericArguments): Promise<TestDirectory>
     runBlockingShellCommand(input: BlockingCommandClientInput): Promise<BlockingShellCommandOutput>
+    runLuaCode(input: LuaCodeClientInput): Promise<RunLuaCodeOutput>
   }
 }
diff --git a/packages/library/src/client/terminal-client.ts b/packages/library/src/client/terminal-client.ts
index aa7eb39..4316563 100644
--- a/packages/library/src/client/terminal-client.ts
+++ b/packages/library/src/client/terminal-client.ts
@@ -1,8 +1,13 @@
 import { createTRPCClient, httpBatchLink, splitLink, unstable_httpSubscriptionLink } from "@trpc/client"
 import type { Terminal } from "@xterm/xterm"
 import "@xterm/xterm/css/xterm.css"
-import type { AppRouter, BlockingCommandClientInput } from "../server/server.js"
-import type { BlockingShellCommandOutput, StartNeovimGenericArguments, TestDirectory } from "../server/types.js"
+import type { AppRouter, BlockingCommandClientInput, LuaCodeClientInput } from "../server/server.js"
+import type {
+  BlockingShellCommandOutput,
+  RunLuaCodeOutput,
+  StartNeovimGenericArguments,
+  TestDirectory,
+} from "../server/types.js"
 import "./style.css"
 import { getTabId, startTerminal } from "./websocket-client.js"
 
@@ -92,4 +97,12 @@ export class TerminalClient {
       tabId: this.tabId,
     })
   }
+
+  public async runLuaCode(input: LuaCodeClientInput): Promise<RunLuaCodeOutput> {
+    await this.ready
+    return this.trpc.neovim.runLuaCode.mutate({
+      luaCode: input.luaCode,
+      tabId: this.tabId,
+    })
+  }
 }
diff --git a/packages/library/src/server/cypress-support/contents.test.ts b/packages/library/src/server/cypress-support/contents.test.ts
index 366d754..51214ad 100644
--- a/packages/library/src/server/cypress-support/contents.test.ts
+++ b/packages/library/src/server/cypress-support/contents.test.ts
@@ -7,9 +7,10 @@ it("should return the expected contents", async () => {
     //
     // This file is autogenerated by tui-sandbox. Do not edit it directly.
     //
-    import type { BlockingCommandClientInput } from "@tui-sandbox/library/dist/src/server/server"
+    import type { BlockingCommandClientInput, LuaCodeClientInput } from "@tui-sandbox/library/dist/src/server/server"
     import type {
       BlockingShellCommandOutput,
+      RunLuaCodeOutput,
       StartNeovimGenericArguments,
     } from "@tui-sandbox/library/dist/src/server/types"
     import type { OverrideProperties } from "type-fest"
@@ -24,6 +25,7 @@ it("should return the expected contents", async () => {
       interface Window {
         startNeovim(startArguments?: MyStartNeovimServerArguments): Promise<NeovimContext>
         runBlockingShellCommand(input: BlockingCommandClientInput): Promise<BlockingShellCommandOutput>
+        runLuaCode(input: LuaCodeClientInput): Promise<RunLuaCodeOutput>
       }
     }
 
@@ -54,6 +56,12 @@ it("should return the expected contents", async () => {
       cy.get("textarea").focus().type(text, options)
     })
 
+    Cypress.Commands.add("runLuaCode", (input: LuaCodeClientInput) => {
+      cy.window().then(async win => {
+        return await win.runLuaCode(input)
+      })
+    })
+
     before(function () {
       // disable Cypress's default behavior of logging all XMLHttpRequests and
       // fetches to the Command Log
@@ -73,6 +81,8 @@ it("should return the expected contents", async () => {
           /** Runs a shell command in a blocking manner, waiting for the command to
            * finish before returning. Requires neovim to be running. */
           runBlockingShellCommand(input: BlockingCommandClientInput): Chainable<BlockingShellCommandOutput>
+
+          runLuaCode(input: LuaCodeClientInput): Chainable<RunLuaCodeOutput>
         }
       }
     }
diff --git a/packages/library/src/server/cypress-support/contents.ts b/packages/library/src/server/cypress-support/contents.ts
index 44b094b..00adcb4 100644
--- a/packages/library/src/server/cypress-support/contents.ts
+++ b/packages/library/src/server/cypress-support/contents.ts
@@ -6,14 +6,15 @@ const __filename = fileURLToPath(import.meta.url)
 export async function createCypressSupportFileContents(): Promise<string> {
   // this is the interface of tui-sandbox as far as cypress in the user's
   // application is concerned
-  let text = ` 
+  let text = `
 /// <reference types="cypress" />
 //
 // This file is autogenerated by tui-sandbox. Do not edit it directly.
 //
-import type { BlockingCommandClientInput } from "@tui-sandbox/library/dist/src/server/server"
+import type { BlockingCommandClientInput, LuaCodeClientInput } from "@tui-sandbox/library/dist/src/server/server"
 import type {
   BlockingShellCommandOutput,
+  RunLuaCodeOutput,
   StartNeovimGenericArguments,
 } from "@tui-sandbox/library/dist/src/server/types"
 import type { OverrideProperties } from "type-fest"
@@ -28,6 +29,7 @@ declare global {
   interface Window {
     startNeovim(startArguments?: MyStartNeovimServerArguments): Promise<NeovimContext>
     runBlockingShellCommand(input: BlockingCommandClientInput): Promise<BlockingShellCommandOutput>
+    runLuaCode(input: LuaCodeClientInput): Promise<RunLuaCodeOutput>
   }
 }
 
@@ -58,6 +60,12 @@ Cypress.Commands.add("typeIntoTerminal", (text: string, options?: Partial<Cypres
   cy.get("textarea").focus().type(text, options)
 })
 
+Cypress.Commands.add("runLuaCode", (input: LuaCodeClientInput) => {
+  cy.window().then(async win => {
+    return await win.runLuaCode(input)
+  })
+})
+
 before(function () {
   // disable Cypress's default behavior of logging all XMLHttpRequests and
   // fetches to the Command Log
@@ -77,6 +85,8 @@ declare global {
       /** Runs a shell command in a blocking manner, waiting for the command to
        * finish before returning. Requires neovim to be running. */
       runBlockingShellCommand(input: BlockingCommandClientInput): Chainable<BlockingShellCommandOutput>
+
+      runLuaCode(input: LuaCodeClientInput): Chainable<RunLuaCodeOutput>
     }
   }
 }
diff --git a/packages/library/src/server/neovim/index.ts b/packages/library/src/server/neovim/index.ts
index d984537..ead37f6 100644
--- a/packages/library/src/server/neovim/index.ts
+++ b/packages/library/src/server/neovim/index.ts
@@ -2,8 +2,13 @@ import assert from "assert"
 import { exec } from "child_process"
 import "core-js/proposals/async-explicit-resource-management.js"
 import util from "util"
-import type { BlockingCommandInput } from "../server.js"
-import type { BlockingShellCommandOutput, StartNeovimGenericArguments, TestDirectory } from "../types.js"
+import type { BlockingCommandInput, LuaCodeInput } from "../server.js"
+import type {
+  BlockingShellCommandOutput,
+  RunLuaCodeOutput,
+  StartNeovimGenericArguments,
+  TestDirectory,
+} from "../types.js"
 import type { TestServerConfig } from "../updateTestdirectorySchemaFile.js"
 import { convertEventEmitterToAsyncGenerator } from "../utilities/generator.js"
 import type { TabId } from "../utilities/tabId.js"
@@ -110,3 +115,29 @@ export async function runBlockingShellCommand(
     throw new Error(`Error running shell blockingCommand (${input.command})`, { cause: e })
   }
 }
+
+export async function runLuaCode(options: LuaCodeInput): Promise<RunLuaCodeOutput> {
+  const neovim = neovims.get(options.tabId.tabId)
+  assert(
+    neovim !== undefined,
+    `Neovim instance for clientId not found - cannot run Lua code. Maybe neovim's not started yet?`
+  )
+  assert(
+    neovim.application,
+    `Neovim application not found for client id ${options.tabId.tabId}. Maybe it's not started yet?`
+  )
+
+  const api = await neovim.state?.client.get()
+  if (!api) {
+    throw new Error(`Neovim API not available for client id ${options.tabId.tabId}. Maybe it's not started yet?`)
+  }
+
+  console.log(`Neovim ${neovim.application.processId()} running Lua code: ${options.luaCode}`)
+  try {
+    const value = await api.lua(options.luaCode)
+    return { value }
+  } catch (e) {
+    console.warn(`Error running Lua code: ${options.luaCode}`, e)
+    throw new Error(`Error running Lua code: ${options.luaCode}`, { cause: e })
+  }
+}
diff --git a/packages/library/src/server/server.ts b/packages/library/src/server/server.ts
index 6fc4411..3e5b16d 100644
--- a/packages/library/src/server/server.ts
+++ b/packages/library/src/server/server.ts
@@ -25,6 +25,10 @@ const blockingCommandInputSchema = z.object({
 export type BlockingCommandClientInput = Except<BlockingCommandInput, "tabId">
 export type BlockingCommandInput = z.infer<typeof blockingCommandInputSchema>
 
+const luaCodeInputSchema = z.object({ tabId: tabIdSchema, luaCode: z.string() })
+export type LuaCodeClientInput = Except<LuaCodeInput, "tabId">
+export type LuaCodeInput = z.infer<typeof luaCodeInputSchema>
+
 /** @private */
 // eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export async function createAppRouter(config: TestServerConfig) {
@@ -72,6 +76,10 @@ export async function createAppRouter(config: TestServerConfig) {
       runBlockingShellCommand: trpc.procedure.input(blockingCommandInputSchema).mutation(async options => {
         return neovim.runBlockingShellCommand(options.signal, options.input, options.input.allowFailure ?? false)
       }),
+
+      runLuaCode: trpc.procedure.input(luaCodeInputSchema).mutation(options => {
+        return neovim.runLuaCode(options.input)
+      }),
     }),
   })
 
diff --git a/packages/library/src/server/types.ts b/packages/library/src/server/types.ts
index dd2a641..c098e6a 100644
--- a/packages/library/src/server/types.ts
+++ b/packages/library/src/server/types.ts
@@ -1,3 +1,5 @@
+import type { VimValue } from "neovim/lib/types/VimValue.js"
+
 /** Describes the contents of the test directory, which is a blueprint for
  * files and directories. Tests can create a unique, safe environment for
  * interacting with the contents of such a directory.
@@ -42,3 +44,8 @@ export type BlockingShellCommandOutput =
       // for now we log the error to the server's console output. It will be
       // visible when running the tests.
     }
+
+export type RunLuaCodeOutput = {
+  value?: VimValue
+  // to catch errors, use pcall() in the Lua code
+}