---
summary: "Nodmix code mode: an opt-in exec/wait tool surface backed by QuickJS-WASI and a hidden run-scoped tool catalog"
title: "Code mode"
sidebarTitle: "Code mode"
read_when:
  - You want to enable Nodmix code mode for an agent run
  - You need to explain why code mode is different from Codex Code mode
  - You are reviewing the exec/wait contract, QuickJS-WASI sandbox, TypeScript transform, or hidden tool-catalog bridge
---

Code mode is an experimental Nodmix agent-runtime feature. It is off by
default. When you enable it, Nodmix changes what the model sees for one run:
instead of exposing every enabled tool schema directly, the model sees only
`exec` and `wait`.

This page documents Nodmix code mode. It is not Codex Code mode. The two
features share a name, but they are implemented by different runtimes and expose
different `exec` contracts:

- Codex Code Mode is enabled for Codex app-server threads unless restricted
  tool policy disables native code mode. It runs in the Codex coding harness,
  where the model writes shell commands through an `exec.command` contract.
- Nodmix code mode is disabled unless `tools.codeMode.enabled: true` is
  configured. It runs in the Nodmix generic agent runtime, where the model
  writes JavaScript or TypeScript programs through an `exec.code` contract.

Codex Code Mode and Codex-native dynamic tool search are stable Codex harness
surfaces. Nodmix code mode is an Nodmix-owned experimental tool-surface
adapter for generic Nodmix runs. It uses `quickjs-wasi`, a hidden Nodmix
tool catalog, and the normal Nodmix tool executor.

## What is this?

Nodmix code mode lets the model write a small JavaScript or TypeScript program
instead of choosing directly from a long list of tools.

When code mode is active:

- The model-visible tool list is exactly `exec` and `wait`.
- `exec` evaluates model-generated JavaScript or TypeScript in a constrained
  QuickJS-WASI worker.
- Normal Nodmix tools are hidden from the model prompt and exposed inside the
  guest program through `ALL_TOOLS` and `tools`.
- Guest code can search the hidden catalog, describe a tool, and call a tool
  through the same Nodmix execution path used by normal agent turns.
- `wait` resumes a suspended code-mode run when nested tool calls are still
  pending.

The important distinction: code mode changes the model-facing orchestration
surface. It does not replace Nodmix tools, plugin tools, MCP tools, auth,
approval policy, channel behavior, or model selection.

## Why is this good?

Code mode makes large tool catalogs easier for models to use.

- Smaller prompt surface: providers receive two control tools instead of dozens
  or hundreds of full tool schemas.
- Better orchestration: the model can use loops, joins, small transforms,
  conditional logic, and parallel nested tool calls inside one code cell.
- Provider neutral: it works for Nodmix, plugin, MCP, and client tools without
  depending on provider-native code execution.
- Existing policy stays in force: nested tool calls still go through Nodmix
  policy, approvals, hooks, session context, and audit paths.
- Clear failure mode: when code mode is explicitly enabled and the runtime is
  unavailable, Nodmix fails closed instead of falling back to broad direct tool
  exposure.

Code mode is especially useful for agents with a large enabled tool catalog or
for workflows where the model repeatedly needs to search, combine, and call
tools before producing an answer.

## How to enable it

Add `tools.codeMode.enabled: true` to the agent or runtime config:

```json5
{
  tools: {
    codeMode: {
      enabled: true,
    },
  },
}
```

The shorthand is also accepted:

```json5
{
  tools: {
    codeMode: true,
  },
}
```

Code mode remains off when `tools.codeMode` is omitted, `false`, or an object
without `enabled: true`.

Use explicit limits when you want tighter bounds:

```json5
{
  tools: {
    codeMode: {
      enabled: true,
      timeoutMs: 10000,
      memoryLimitBytes: 67108864,
      maxOutputBytes: 65536,
      maxSnapshotBytes: 10485760,
      maxPendingToolCalls: 16,
      snapshotTtlSeconds: 900,
      searchDefaultLimit: 8,
      maxSearchLimit: 50,
    },
  },
}
```

To confirm the model payload shape while debugging, run the Gateway with
targeted logging:

```bash
NODMIX_DEBUG_CODE_MODE=1 \
NODMIX_DEBUG_MODEL_TRANSPORT=1 \
NODMIX_DEBUG_MODEL_PAYLOAD=tools \
nodmix gateway
```

With code mode active, the logged model-facing tool names should be `exec` and
`wait`. If you need the redacted provider payload, add
`NODMIX_DEBUG_MODEL_PAYLOAD=full-redacted` for a short debugging session.

## Technical tour

The rest of this page describes the runtime contract and implementation details.
It is intended for maintainers, plugin authors debugging tool exposure, and
operators validating high-risk deployments.

## Runtime status

- Runtime: [`quickjs-wasi`](https://github.com/vercel-labs/quickjs-wasi).
- Default state: disabled.
- Stability: experimental Nodmix surface; Codex Code mode is a separate stable
  Codex harness surface.
- Target surface: generic Nodmix agent runs.
- Security posture: model code is hostile.
- User-facing promise: enabling code mode never silently falls back to broad
  direct tool exposure.

## Scope

Code mode owns the model-facing orchestration shape for a prepared run. It does
not own model selection, channel behavior, auth, tool policy, or tool
implementations.

In scope:

- model-visible `exec` and `wait` tool definitions
- hidden tool catalog construction
- JavaScript and TypeScript guest execution
- QuickJS-WASI worker runtime
- host callbacks for catalog search, schema describe, and tool call
- resumable state for suspended guest programs
- output, timeout, memory, pending-call, and snapshot limits
- telemetry and trajectory projection for nested tool calls

Out of scope:

- provider-native remote code execution
- shell execution semantics
- changing existing tool authorization
- persistent user-authored scripts
- package manager, file, network, or module access in guest code
- direct reuse of Codex Code mode internals

Provider-owned tools such as remote Python sandboxes remain separate tools. See
[Code execution](/tools/code-execution).

## Terms

**Code mode** is the Nodmix runtime mode that hides normal model tools and
exposes only `exec` and `wait`.

**Guest runtime** is the QuickJS-WASI JavaScript VM that evaluates model code.

**Host bridge** is the narrow JSON-compatible callback surface from guest code
back into Nodmix.

**Catalog** is the run-scoped list of effective tools after normal tool policy,
plugin, MCP, and client-tool resolution.

**Nested tool call** is a tool call made from guest code through the host bridge.

**Snapshot** is serialized QuickJS-WASI VM state saved so `wait` can continue a
suspended code-mode run.

## Configuration

`tools.codeMode.enabled` is the activation gate. Setting other code-mode fields
does not enable the feature.

Supported fields:

- `enabled`: boolean. Default `false`. Enables code mode only when `true`.
- `runtime`: `"quickjs-wasi"`. Only supported runtime.
- `mode`: `"only"`. Exposes `exec` and `wait`, hides normal model tools.
- `languages`: array of `"javascript"` and `"typescript"`. Default includes
  both.
- `timeoutMs`: wall-clock cap for one `exec` or `wait`. Default `10000`.
  Runtime clamp: `100` to `60000`.
- `memoryLimitBytes`: QuickJS heap cap. Default `67108864`. Runtime clamp:
  `1048576` to `1073741824`.
- `maxOutputBytes`: cap for returned text, JSON, and logs. Default `65536`.
  Runtime clamp: `1024` to `10485760`.
- `maxSnapshotBytes`: cap for serialized VM snapshots. Default `10485760`.
  Runtime clamp: `1024` to `268435456`.
- `maxPendingToolCalls`: cap for concurrent nested tool calls. Default `16`.
  Runtime clamp: `1` to `128`.
- `snapshotTtlSeconds`: how long a suspended VM can be resumed. Default `900`.
  Runtime clamp: `1` to `86400`.
- `searchDefaultLimit`: default hidden-catalog search result count. Default `8`.
  Runtime clamps this to `maxSearchLimit`.
- `maxSearchLimit`: maximum hidden-catalog search result count. Default `50`.
  Runtime clamp: `1` to `50`.

If code mode is enabled but QuickJS-WASI cannot load, Nodmix fails closed for
that run. It does not silently expose normal tools as a fallback.

## Activation

Code mode is evaluated after the effective tool policy is known and before the
final model request is assembled.

Activation order:

1. Resolve the agent, model, provider, sandbox, channel, sender, and run policy.
2. Build the effective Nodmix tool list.
3. Add eligible plugin, MCP, and client tools.
4. Apply allow and deny policy.
5. If `tools.codeMode.enabled` is false, continue with normal tool exposure.
6. If enabled and tools are active for the run, register the effective tools in
   the code-mode catalog.
7. Remove all normal tools from the model-visible tool list.
8. Add code-mode `exec` and `wait`.

Runs that intentionally have no tools, such as raw model calls, `disableTools`,
or an empty allowlist, do not activate the code-mode surface even if the config
contains `tools.codeMode.enabled: true`.

The code-mode catalog is run-scoped. It must not leak tools from another agent,
session, sender, or run.

## Model-visible tools

When code mode is active, the model sees exactly these top-level tools:

- `exec`
- `wait`

All other enabled tools are hidden from the model-facing tool list and registered
in the code-mode catalog.

The model should use `exec` for tool orchestration, data joining, loops,
parallel nested calls, and structured transformations. The model should use
`wait` only when `exec` returns a resumable `waiting` result.

## `exec`

`exec` starts a code-mode cell and returns one result. The input code is model
generated and must be treated as hostile.

Input:

```typescript
type CodeModeExecInput = {
  code?: string;
  command?: string;
  language?: "javascript" | "typescript";
};
```

Input rules:

- One of `code` or `command` must be non-empty.
- `code` is the documented model-facing field.
- `command` is accepted as an exec-compatible alias for hook policies and
  trusted rewrites; when both are present, the values must match.
- Outer code-mode `exec` hook events include `toolKind: "code_mode_exec"` and
  include `toolInputKind: "javascript" | "typescript"` when the input language
  is known, so policies can distinguish code-mode cells from shell-style `exec`
  calls that share the same tool name.
- `language` defaults to `"javascript"`.
- If `language` is `"typescript"`, Nodmix transpiles before evaluation.
- `exec` rejects `import`, `require`, dynamic import, and module-loader patterns
  in v1.
- `exec` does not expose the normal shell `exec` implementation recursively.

Result:

```typescript
type CodeModeResult = CodeModeCompletedResult | CodeModeWaitingResult | CodeModeFailedResult;

type CodeModeCompletedResult = {
  status: "completed";
  value: unknown;
  output?: CodeModeOutput[];
  telemetry: CodeModeTelemetry;
};

type CodeModeWaitingResult = {
  status: "waiting";
  runId: string;
  reason: "pending_tools" | "yield";
  pendingToolCalls?: CodeModePendingToolCall[];
  output?: CodeModeOutput[];
  telemetry: CodeModeTelemetry;
};

type CodeModeFailedResult = {
  status: "failed";
  error: string;
  code?: CodeModeErrorCode;
  output?: CodeModeOutput[];
  telemetry: CodeModeTelemetry;
};
```

`exec` returns `waiting` when the QuickJS VM suspends with resumable state. The
result includes a `runId` for `wait`.

`exec` returns `completed` only when the guest VM has no pending work and the
final value is JSON-compatible after Nodmix's output adapter runs.

## `wait`

`wait` continues a suspended code-mode VM.

Input:

```typescript
type CodeModeWaitInput = {
  runId: string;
};
```

The output is the same `CodeModeResult` union returned by `exec`.

`wait` exists because nested Nodmix tools can be slow, interactive, approval
gated, or stream partial updates. The model should not need to keep one long
`exec` call open while the host waits for external work.

QuickJS-WASI snapshot and restore is the v1 resume mechanism:

1. `exec` evaluates code until completion, failure, or suspension.
2. On suspension, Nodmix snapshots the QuickJS VM and records pending host
   work.
3. When pending work settles, `wait` restores the VM snapshot.
4. Nodmix re-registers host callbacks by stable names.
5. Nodmix delivers nested tool results into the restored VM.
6. Nodmix drains QuickJS pending jobs.
7. `wait` returns `completed`, `failed`, or another `waiting` result.

Snapshots are runtime state, not user artifacts. They are size-limited, expired,
and scoped to the run and session that created them.

`wait` fails when:

- `runId` is unknown.
- the snapshot expired.
- the parent run or session was aborted.
- the caller is not in the same run/session scope.
- QuickJS-WASI restore fails.
- restoring would exceed configured limits.

## Guest runtime API

The guest runtime exposes a small global API:

```typescript
declare const ALL_TOOLS: ToolCatalogEntry[];
declare const tools: ToolCatalog;

declare function text(value: unknown): void;
declare function json(value: unknown): void;
declare function yield_control(reason?: string): Promise<void>;
```

`ALL_TOOLS` is compact metadata for the run-scoped catalog. It does not contain
full schemas by default.

```typescript
type ToolCatalogEntry = {
  id: string;
  name: string;
  label?: string;
  description: string;
  source: "nodmix" | "plugin" | "mcp" | "client";
  sourceName?: string;
};
```

Full schema is loaded only on demand:

```typescript
type ToolCatalogEntryWithSchema = ToolCatalogEntry & {
  parameters: unknown;
};
```

Catalog helpers:

```typescript
type ToolCatalog = {
  search(query: string, options?: { limit?: number }): Promise<ToolCatalogEntry[]>;
  describe(id: string): Promise<ToolCatalogEntryWithSchema>;
  call(id: string, input?: unknown): Promise<unknown>;
  [safeToolName: string]: unknown;
};
```

Convenience tool functions are installed only for unambiguous safe names:

```typescript
const files = await tools.search("read local file");
const fileRead = await tools.describe(files[0].id);
const content = await tools.call(fileRead.id, { path: "README.md" });

// If the hidden catalog has an unambiguous `web_search` entry:
const hits = await tools.web_search({ query: "Nodmix code mode" });
```

The guest runtime must not expose host objects directly. Inputs and outputs cross
the bridge as JSON-compatible values with explicit size caps.

## Output API

`text(value)` appends human-readable output to the `output` array.

`json(value)` appends a structured output item after JSON-compatible
serialization.

The guest code's final returned value becomes `value` in a `completed` result.

Output item:

```typescript
type CodeModeOutput = { type: "text"; text: string } | { type: "json"; value: unknown };
```

Output rules:

- output order matches guest calls
- output is capped by `maxOutputBytes`
- non-serializable values are converted to plain strings or errors
- binary values are not supported in v1
- images and files travel through ordinary Nodmix tools, not through the
  code-mode bridge

## Tool catalog

The hidden catalog includes tools after effective policy filtering:

1. Nodmix core tools.
2. Bundled plugin tools.
3. External plugin tools.
4. MCP tools.
5. Client-provided tools for the current run.

Catalog ids are stable within one run and deterministic across equivalent tool
sets when possible.

Recommended id shape:

```text
<source>:<owner>:<tool-name>
```

Examples:

```text
nodmix:core:message
plugin:browser:browser_request
mcp:github:create_issue
client:app:select_file
```

The catalog omits code-mode control tools:

- `exec`
- `wait`
- `tool_search_code`
- `tool_search`
- `tool_describe`
- `tool_call`

This prevents recursion and keeps the model-facing contract narrow.

## Tool Search interaction

Code mode supersedes the Nodmix Tool Search model surface for runs where it is
active.

When `tools.codeMode.enabled` is true and code mode activates:

- Nodmix does not expose `tool_search_code`, `tool_search`, `tool_describe`,
  or `tool_call` as model-visible tools.
- The same cataloging idea moves inside the guest runtime.
- The guest runtime receives compact `ALL_TOOLS` metadata and search, describe,
  and call helpers.
- Nested calls dispatch through the same Nodmix executor path that Tool Search
  uses.

The existing [Tool Search](/tools/tool-search) page describes the Nodmix compact
catalog bridge. Code mode is the generic Nodmix alternative for runs that can
use `exec` and `wait`.

## Tool names and collisions

The model-visible `exec` tool is the code-mode tool. If the normal Nodmix
shell `exec` tool is enabled, it is hidden from the model and cataloged like any
other tool.

Inside the guest runtime:

- `tools.call("nodmix:core:exec", input)` can call the shell exec tool if
  policy allows it.
- `tools.exec(...)` is installed only if the shell exec catalog entry has an
  unambiguous safe name.
- the code-mode `exec` tool is never recursively available through `tools`.

If two tools normalize to the same safe convenience name, Nodmix omits the
convenience function and requires `tools.call(id, input)`.

## Nested tool execution

Every nested tool call crosses the host bridge and re-enters Nodmix.

Nested execution preserves:

- active agent id
- session id and session key
- sender and channel context
- sandbox policy
- approval policy
- plugin `before_tool_call` hooks
- abort signal
- streaming updates where available
- trajectory and audit events

Nested calls project into the transcript as real tool calls so support bundles
can show what happened. The projection identifies the parent code-mode tool call
and the nested tool id.

Parallel nested calls are allowed up to `maxPendingToolCalls`.

## Runtime state

Each code-mode run has a state machine:

- `running`: VM is executing or nested calls are in flight.
- `waiting`: VM snapshot exists and can be resumed with `wait`.
- `completed`: final value returned; snapshot deleted.
- `failed`: error returned; snapshot deleted.
- `expired`: snapshot or pending state exceeded retention; cannot resume.
- `aborted`: parent run/session cancelled; snapshot deleted.

State is scoped by agent run, session, and tool call id. A `wait` call from a
different run or session fails.

Snapshot storage is bounded:

- maximum snapshot bytes per run
- maximum live snapshots per process
- snapshot TTL
- cleanup on run end
- cleanup on Gateway shutdown where persistence is not supported

## QuickJS-WASI runtime

Nodmix loads `quickjs-wasi` as a direct dependency in the owning package. The
runtime does not rely on a transitive copy installed for proxy, PAC, or other
unrelated dependencies.

Runtime responsibilities:

- compile or load the QuickJS-WASI WebAssembly module
- create one isolated VM per code-mode run or resume
- register host callbacks by stable names
- set memory and interrupt limits
- evaluate JavaScript
- drain pending jobs
- snapshot suspended VM state
- restore snapshots for `wait`
- dispose VM handles and snapshots after terminal states

The runtime executes outside Nodmix's main event loop in a worker. A guest
infinite loop must not block the Gateway process indefinitely.

## TypeScript

TypeScript support is a source transform only:

- accepted input: one TypeScript code string
- output: JavaScript string evaluated by QuickJS-WASI
- no typechecking
- no module resolution
- no `import` or `require` in v1
- diagnostics are returned as `failed` results

The TypeScript compiler is loaded lazily only for TypeScript cells. Plain
JavaScript cells and disabled code mode do not load the compiler.

The transform should preserve useful line numbers where feasible.

## Security boundary

Model code is hostile. The runtime uses defense in depth:

- run QuickJS-WASI outside the main event loop
- load `quickjs-wasi` as a direct dependency, not through Codex or a transitive
  package
- no filesystem, network, subprocess, module import, environment variables, or
  host global objects in the guest
- use QuickJS memory and interrupt limits
- enforce parent-process wall-clock timeout
- enforce output, snapshot, log, and pending-call caps
- serialize host bridge values through a narrow JSON adapter
- convert host errors into plain guest errors, never host realm objects
- drop snapshots on timeout, abort, session end, or expiry
- reject recursive access to `exec`, `wait`, and Tool Search control tools
- prevent convenience-name collisions from shadowing catalog helpers

The sandbox is one security layer. Operators can still need OS-level hardening
for high-risk deployments.

## Error codes

```typescript
type CodeModeErrorCode =
  | "runtime_unavailable"
  | "invalid_config"
  | "invalid_input"
  | "unsupported_language"
  | "typescript_transform_failed"
  | "module_access_denied"
  | "timeout"
  | "memory_limit_exceeded"
  | "output_limit_exceeded"
  | "snapshot_limit_exceeded"
  | "snapshot_expired"
  | "snapshot_restore_failed"
  | "too_many_pending_tool_calls"
  | "nested_tool_failed"
  | "aborted"
  | "internal_error";
```

Errors returned to the guest are plain data. Host `Error` instances, stack
objects, prototypes, and host functions do not cross into QuickJS.

## Telemetry

Code mode reports:

- visible tool names sent to the model
- hidden catalog size and source breakdown
- `exec` and `wait` counts
- nested search, describe, and call counts
- nested tool ids called
- timeout, memory, snapshot, and output cap failures
- snapshot lifecycle events

Telemetry must not include secrets, raw environment values, or unredacted tool
inputs beyond existing Nodmix trajectory policy.

## Debugging

Use targeted model transport logging when code mode behaves differently from a
normal tool run:

```bash
NODMIX_DEBUG_CODE_MODE=1 \
NODMIX_DEBUG_MODEL_TRANSPORT=1 \
NODMIX_DEBUG_MODEL_PAYLOAD=tools \
NODMIX_DEBUG_SSE=events \
nodmix gateway
```

For payload-shape debugging, use `NODMIX_DEBUG_MODEL_PAYLOAD=full-redacted`.
This logs a capped, redacted JSON snapshot of the model request; it should only
be used while debugging because prompts and message text can still appear.

For stream debugging, use `NODMIX_DEBUG_SSE=peek` to log the first five
redacted SSE events. Code mode also fails closed if the final provider payload
does not contain exactly `exec` and `wait` after the code-mode surface has
activated.

## Implementation layout

Implementation units:

- config contract: `tools.codeMode`
- catalog builder: effective tools to compact entries and id map
- model-surface adapter: replace visible tools with `exec` and `wait`
- QuickJS-WASI runtime adapter: load, eval, snapshot, restore, dispose
- worker supervisor: timeout, abort, crash isolation
- bridge adapter: JSON-safe host callbacks and result delivery
- TypeScript transform adapter
- snapshot store: TTL, size caps, run/session scoping
- trajectory projection for nested tool calls
- telemetry counters and diagnostics

The implementation reuses catalog and executor concepts from Tool Search, but
does not use the `node:vm` child as the sandbox.

## Validation checklist

Code mode coverage should prove:

- disabled config leaves existing tool exposure unchanged
- object config without `enabled: true` leaves code mode disabled
- enabled config exposes only `exec` and `wait` to the model when tools are
  active for the run
- raw no-tool runs, `disableTools`, and empty allowlists do not trigger code-mode
  payload enforcement
- all effective tools appear in `ALL_TOOLS`
- denied tools do not appear in `ALL_TOOLS`
- `tools.search`, `tools.describe`, and `tools.call` work for Nodmix tools
- Tool Search control tools are hidden from both the model surface and the hidden
  catalog
- nested calls preserve approval and hook behavior
- shell `exec` is hidden from the model but callable by catalog id when allowed
- recursive code-mode `exec` and `wait` are not callable from guest code
- TypeScript input is transformed and evaluated without loading TypeScript on
  disabled or JavaScript-only paths
- `import`, `require`, filesystem, network, and environment access fail
- infinite loops time out and cannot block the Gateway
- memory cap failures terminate the guest VM
- output and snapshot caps are enforced for completed and suspended calls
- `wait` resumes a suspended snapshot and returns the final value
- expired, aborted, wrong-session, and unknown `runId` values fail
- transcript replay and persistence preserve code-mode control calls
- transcript and telemetry show nested tool calls clearly

## E2E test plan

Run these as integration or end-to-end tests when changing the runtime:

1. Start a Gateway with `tools.codeMode.enabled: false`.
2. Send an agent turn with a small direct tool set.
3. Assert the model-visible tools are unchanged.
4. Restart with `tools.codeMode.enabled: true`.
5. Send an agent turn with Nodmix, plugin, MCP, and client test tools.
6. Assert the model-visible tool list is exactly `exec`, `wait`.
7. In `exec`, read `ALL_TOOLS` and assert the effective test tools are present.
8. In `exec`, call `tools.search`, `tools.describe`, and `tools.call`.
9. Assert denied tools are absent and cannot be called by guessed id.
10. Start a nested tool call that resolves after `exec` returns `waiting`.
11. Call `wait` and assert the restored VM receives the tool result.
12. Assert the final answer contains output produced after restore.
13. Assert timeout, abort, and snapshot expiry clean up runtime state.
14. Export trajectory and assert nested calls are visible under the parent
    code-mode call.

Docs-only changes to this page should still run `pnpm check:docs`.

## Related

- [Tool Search](/tools/tool-search)
- [Agent runtimes](/concepts/agent-runtimes)
- [Exec tool](/tools/exec)
- [Code execution](/tools/code-execution)
