Codemode
Thecodemode tool lets the model write a JavaScript script that calls Atomic’s other tools and runs non-LLM models, such as classifiers and image models. Only the script’s output reaches the model, so a script can run calls in parallel and filter large results before the model sees them. To turn it on, see codemode in Built-in tools.
Scripts
The tool input is raw JavaScript source, not JSON and not a markdown code fence. It runs as the body of an async function in a QuickJS sandbox, so top-levelawait and return work. The sandbox has no Node APIs, file system, network, or timers; scripts reach the outside world only through tools and models.
A script may start with an options line:
max_output_tokens(default 10000) limits the output. Longer output keeps its start and end, and the full text is written to a temp file whose path is included in the result.timeout_msis a hard deadline for the whole script. It is unset by default. Image generation can take minutes, so do not set a short deadline for scripts that generate images.
Script completed or Script failed, the wall time, and the output. A failed script keeps its partial output, followed by Script error: and the error. Tool calls are real: calls made before a failure are not undone. Calls still running when the script ends are cancelled, and unawaited promises are discarded.
Globals
Call tools
Every tool the session can call is a method oftools, named by its identifier: characters that are not valid in a JavaScript identifier become _, so the MCP tool mcp__dev-docs__search is tools.mcp__dev_docs__search. Each method takes one object with the tool’s arguments.
What a call resolves to depends on the tool:
- Tools with an output schema resolve to a structured value.
bashresolves to{ output, truncated, full_output_path?, exit_code, wall_time_seconds }, also for non-zero exit codes. Itsoutputis not limited to what the model sees directly: it holds up to 1 MiB, and longer output keeps its first and last 512 KiB around an omission marker, withtruncatedset and the full output infull_output_path. - MCP tools resolve to their
CallToolResult, includingisErrorandstructuredContent. - Other tools, such as
read,edit, andwrite, resolve to their text output.
Error that carries the tool’s error text. Use Promise.allSettled() to keep the results of the calls that succeed. Reading a tool that does not exist throws an error that names the close matches, so tools.Bash suggests tools.bash; check for a tool with "name" in tools.
The codemode description lists tools with their TypeScript declarations, grouped by namespace (for example one MCP server). Tools with deferred exposure are not listed, so the description stays the same while they register. Listed declarations share a budget of 3000 estimated tokens (codemode.inlineBudget in settings). Scripts find the other tools with searchTools(), describeTool(), describeNamespace(), or by filtering ALL_TOOLS.
While codemode is active, codemode.mode in settings decides how the other tools are presented. With on (default) declared tools stay declared, and their descriptions say in one line how scripts call them and what the call resolves to. With only they are hidden from the model and listed in the codemode description instead, so the model calls them through scripts.
Store values
store(key, value) keeps a JSON value under a string key for later codemode calls; storing undefined deletes the key. load(key) returns the value, or undefined. Writes are kept only when the script succeeds: each successful script that stores values appends a codemode-store custom entry to the session, so resumed sessions keep the values and each branch sees only the values written on its path.
The store is for small state such as IDs, cursors, or summaries. One value may have at most 262144 characters of JSON and all values together at most 1048576. Do not store image data; show images with image() or write them to a file with a tool.
Models
models reaches the model catalog and runs non-LLM models with the session’s credentials: classifiers, which answer typed questions about JSON state, and image models, which generate images. Chat models are listed but cannot be run from scripts. Classifier models include TypeSafe Jev and local llama.cpp models; image models include OpenRouter’s, such as google/gemini-2.5-flash-image and black-forest-labs/flux.2-pro, which use the same OPENROUTER_API_KEY or /login credential as its chat models. Neither kind appears in /model.
classify() and generateImages() use only the provider and id of model, so { provider, id } works as well, and a script-supplied baseUrl or headers never receive the credentials. They do not throw on provider errors: check stopReason and errorMessage. A malformed model or context does throw, with the expected shape in the message; an unknown or mistyped model points to models.getAvailableOfType(). At most four such calls run at once per script; more calls wait for a free slot, so Promise.all() over many items is fine. Their usage is added to the codemode tool result and counts toward the session cost.
Model IDs differ between providers. Use models.getAvailableOfType(type) to find the IDs that work with the current credentials.
Classify
classify() once per item. This script sorts feedback messages, for example ones a tool returned earlier in the script:
Generate images
image(block). Do not print data with text(), console, or return: it is large and the model cannot read it as text. A script that generates images without showing any gets a note saying so. Generated images are not saved to disk; to keep one, write it to a file with a tool.
ctx.modelRegistry.classify() and ctx.modelRegistry.generateImages(), without codemode.
Limits
- A script’s VM has 256 MB of memory. Running out throws
InternalError: out of memory; filter or aggregate large data instead of accumulating it. - A script that waits on a promise that can never settle (no tool call pending) fails immediately, since there are no timers.
- Scripts cannot start other
codemodescripts.