plimsoll-client for Python

A Python client for plimsolld, the plimsoll sandbox daemon. It runs JavaScript snippets, multi-file projects and compiled simulators (module runs) on a daemon, opens sessions, and makes every check the Go client in client/ makes on what comes back. It uses the Python standard library only and needs Python 3.10 or later.

It speaks Connect's JSON protocol over HTTP/1.1: each call is one HTTP POST of a JSON message (Connect protocol reference (EXTERNAL · official docs ↗)), with the message in protobuf's JSON form (ProtoJSON format (EXTERNAL · official docs ↗)). The messages are defined in proto/plimsoll/v1/sandbox.proto.

Install

From PyPI (plimsoll-client (EXTERNAL · package index ↗)):

pip install plimsoll-client

Or from a checkout of this repository: pip install ./clients/python.

The distribution is plimsoll-client; the import package is plimsoll_client.

Use

from plimsoll_client import Client

c = Client("http://127.0.0.1:8746", token="...")  # the token needs the code:run scope
info = c.describe()
print(info.provider, info.isolation)

r = c.run_javascript("console.log(6*7)", timeout=10.0, minimum_isolation="process")
print(r.exit_code, r.stdout_text, r.record.sha256)

p = c.run_project(
    files={"main.js": "console.log(require('./lib.js'))", "lib.js": "module.exports = 42"},
    steps=["node main.js"],
    artifacts=[],
    minimum_isolation="container",
)
print(p.outcome, [s.stdout_text for s in p.steps])

with c.open_session(minimum_isolation="container") as s:
    s.run_javascript("require('fs').writeFileSync('/tmp/a', '1')")
    s.run_javascript("console.log(require('fs').readFileSync('/tmp/a', 'utf8'))")
    # Cells run in an interpreter the session keeps alive, so state survives calls.
    s.run_cell("import csv\nrows = list(csv.reader(open('data.csv')))", files={"data.csv": "a,b\n1,2\n"})
    print(s.run_cell("len(rows)").stdout_text)  # 2: the last expression is printed
summary = s.close()  # the call count and the last record's digest; closing again is harmless

run_cell(code, language="python", files=...) runs code in the session's interpreter for "python" or "javascript". files are written into the session's work directory, the interpreter's working directory, before the code runs: the way to hand a cell data from somewhere else, such as another tool's output. The result's exit_code is 0 when the code ran, 1 when it raised (the error is on stderr) and 124 at the deadline; interpreter_started says this call began with a fresh interpreter, so nothing defined earlier exists. Python cells need python3 in the daemon's image: describe() lists the languages its startup checks proved on project_environment.languages.

An app that serves many users on one token passes open_session(owner=user_id). A daemon with SANDBOX_MAX_SESSIONS_PER_OWNER then holds each user to that many open sessions across every process of the app, closing the user's least recently used idle session to open a new one; a call on the closed session raises SessionEndedError with reason == "replaced", marked not dispatched, so it is safe to run again in a new session. The ID never leaves the process: the daemon gets an HMAC-SHA256 of it (a keyed hash that cannot be reversed) under a key derived from the client's token, so a daemon, which stores only each token's SHA-256, cannot test a guessed ID.

For a framework that needs a bounded code call without a persistent interpreter, plimsoll_client.execution.CodeExecutor runs Python or JavaScript in a fresh project:

from plimsoll_client import Client
from plimsoll_client.execution import CodeExecutor

executor = CodeExecutor(Client("http://127.0.0.1:8746"))
result = executor.execute_code("print(sum([1, 2, 3]))", language="python")
print(result.steps[0].stdout_text)

The project image must contain the selected interpreter and its dependencies. The default isolation floor is kernel (verified gVisor or a stronger VM boundary). The default 30-second run budget bounds interactive calculations below the daemon's five-minute ceiling; both are explicit constructor options. files supplies text files, and artifacts names output files to capture. .plimsoll/ is reserved for the helper's script. The helper returns the checked ProjectResult unchanged, keeps typed errors and never retries or installs packages. Each call starts fresh.

AsyncClient and AsyncSession in the same package take the same arguments and run each call in a worker thread (asyncio.to_thread), for async agent frameworks. Cancelling an awaiting task cancels its request too:

• Not sent yet (a session call waiting for the one before it, say): it is never sent, and the call ends in RequestCanceledError marked not dispatched (reason request).
• In flight (connecting, in the TLS handshake, sent or waiting for its answer): the connection is shut down, so the worker thread returns at once instead of waiting out request_timeout. The error is unmarked: the daemon may have received the request and run it. A session whose call was cut sends nothing more, since it can no longer follow the daemon's chain of records: open a new one.

Two calls run to their end instead. open_session: cutting it after the daemon had answered would leave a session nobody holds the ID of, holding its place until it expired, so the open finishes in its thread and a session it opens after the cancel is closed. And AsyncSession.close, which is what releases the session.

The synchronous client takes the same control explicitly: pass a CancelHandle as cancel= to describe, run_javascript, run_project, run_module or a session's calls, and call handle.cancel() from any thread. One handle can cover several requests; once cancelled it refuses every later one, with nothing sent. Name resolution is not interrupted. Whether the daemon stops code it already started depends on its provider: the daemon's handler passes the provider a context that ends when the connection closes, and a provider that honors it stops the run.

Terms used below:

• An isolation tier is how strong the walls around a run are: process, container, kernel or vm, weakest first. A tier is the daemon's configuration and provider evidence, never runtime attestation (cryptographic proof of what a machine runs).
• A floor (minimum_isolation) is the weakest tier a request accepts.
• Dispatch is the moment the daemon hands the code over to start running.
• A run record is the daemon's statement of one run: SHA-256 digests of the request as sent and the result as returned, the evidence the run executed under, and when (docs/run-records.md).
• A session is one sandbox kept open for many calls: files persist between calls, and no process does except the interpreter the session keeps for its cells (docs/sessions.md). Code an earlier call ran can change what later calls see, and a call that names a grant_profile needs a profile that allows sessions (what a session gives up). A session is one trust domain: plimsoll ties it to the credential that opened it, not to the users behind that credential, so a service running many users' code through one credential must give each user (and each conversation or job) a session of their own, chosen by identities it verified (who may share a session).

Results are frozen dataclasses. Guest output (stdout, stderr, artifact contents) is bytes, because a guest can print any byte sequence and the record covers the exact bytes; stdout_text and stderr_text decode it as UTF-8 with invalid sequences replaced. A non-zero exit_code is a normal result (the guest's code failed), not an error. Durations that come back are whole milliseconds (duration_ms); durations you pass in (timeout, request_timeout, a session's lifetime) are seconds.

Google ADK executor

plimsoll_client.adk.PlimsollCodeExecutor implements Google ADK's Python code-block interface over the shared fresh-execution helper. Install it with its extra, pip install 'plimsoll-client[adk]' (0.20.0 and later; 0.19.0 has no extras), or from a checkout with pip install './clients/python[adk]'.

from plimsoll_client import Client
from plimsoll_client.adk import PlimsollCodeExecutor

executor = PlimsollCodeExecutor(client=Client(PLIMSOLL_URL, token=TOKEN))
# Supply executor as your ADK Agent's code_executor.

Each block gets a fresh Python sandbox. The default floor is kernel; stateful mode is refused. Encoded text inputs and raw byte-valued output artifacts follow ADK's file conventions. ADK consumes its native text result; result.execution retains the complete checked ProjectResult. Infrastructure errors propagate without replay. See Google ADK guide (EXTERNAL · official docs ↗) for the CSV optimization limitation, bounded error handling and a no-spend local example.

Agno and CrewAI tools

Two optional modules give an agent one code tool over CodeExecutor (plimsoll_run_code in both): plimsoll_client.agno.PlimsollTools, an Agno toolkit (Agno toolkits (EXTERNAL · official docs ↗)), and plimsoll_client.crewai.PlimsollCodeTool, a CrewAI tool (CrewAI custom tools (EXTERNAL · official docs ↗)). Each is imported only when used, so the client keeps no dependencies; install the framework with the extra of the same name:

The crewai extra installs CrewAI, which installs ChromaDB for its own memory and knowledge features. Every ChromaDB release up to 1.5.9, the latest on 2026-10-08, is affected by advisories against a running Chroma server's HTTP API, with no fixed release (GHSA-f4j7-r4q5-qw2c and three others). Installing the library starts no server, and this tool configures no CrewAI memory, knowledge or embedder, so nothing here runs ChromaDB; if your own crew enables those features, read those advisories first.

pip install 'plimsoll-client[agno]'     # or 'plimsoll-client[crewai]'; 0.20.0 and later

from plimsoll_client import Client
from plimsoll_client.execution import CodeExecutor

executor = CodeExecutor(Client("https://plimsoll.internal:8746", token=TOKEN))

# Agno
from agno.agent import Agent
from plimsoll_client.agno import PlimsollTools
agent = Agent(model=..., tools=[PlimsollTools(executor)])

# CrewAI
from crewai import Agent
from plimsoll_client.crewai import PlimsollCodeTool
agent = Agent(role=..., goal=..., backstory=..., tools=[PlimsollCodeTool(executor)])

Recorded calls through each tool, from a CSV sum to an answer lost after the code may have run, replay on its integration page: Agno: see a run, INTERNAL · plimsoll site → and CrewAI: see a run, INTERNAL · plimsoll site →.

The model calls the tool with code, language ("python" or "javascript", the first of the tool's languages by default) and input_files, a list of {path, content} text files written into the working directory first. Agno reserves a tool parameter named files for the media it passes in and leaves it out of the schema, which is why the parameter is input_files in both tools. The tool answers with JSON:

• ran: true: the code ran; exit_code, timed_out, stdout, stderr and truncated are the guest's, with a non-zero exit as an ordinary result. isolation is the tier it ran behind and record_sha256 the digest of the run record the client checked.
• ran: false: plimsoll refused before anything ran, and refused says why (request or unsupported for something the model can change; isolation, environment, capacity, permission or protocol for the operator, which the tool also logs to the plimsoll_client logger).
• ran: "unknown": an error after which the code may have run. The tool does not retry it, since a second run could repeat what the first did.

What the operator sets, and what the tools do not do:

• The daemon. It must run projects, with python3 (and node, to offer JavaScript) in its project image, such as plimsoll/sandbox-python from make docker-images. Offer only the languages the image runs (languages=("python",)). The sandbox has no network and nothing is installed at run time: the libraries a model may import are the ones built into the image (docs/guest-dependencies.md).
• Isolation. CodeExecutor's floor defaults to kernel: a daemon on docker under runc (container tier) refuses every call until it runs gVisor or the executor is built with minimum_isolation="container", which is for development on your own code only.
• Nothing persists. Every call is a fresh sandbox: a variable, import or file from an earlier call is gone, and the tool's description tells the model so.
• Cancellation. The async paths (agent.arun, a CrewAI tool's arun) run the call in a worker thread with a CancelHandle that is cancelled with the await. Cancelled before Run is sent (the daemon's Describe still answering, say), the call never sends it. Cancelled with Run in flight, the connection is cut and the worker thread ends at once rather than at the executor's timeout; the code may have run, and the daemon stops it only if its provider honors the closed connection (above, under AsyncClient).
• CrewAI's tool cache. A crew that opts into CrewAI's tool cache (Crew(cache=True); off by default) looks a call up in that cache by tool name and arguments before calling the tool, whatever the tool's cache_function says, so another tool of the same name could answer for this one with nothing run. The tool never writes to the cache, and constructing one makes every read of CrewAI's CacheHandler miss for its name (one process-wide wrapper of CacheHandler.read, which changes nothing for other tools), so CrewAI always calls it. A cache handler of your own that overrides read is not covered: turn caching off for such a crew (cache=False).
• JavaScript is an ES module. A JavaScript call runs as an ES module: import, not require.
• CrewAI has no interpreter of its own any more. Since April 2026 an agent's allow_code_execution only warns and points to hosted sandboxes (checked in CrewAI 1.15.23); this tool is the self-hosted option.

What the client checks

• The base URL. It must be an absolute http or https URL with no user name, password, query or fragment. Cleartext http is refused for any host that is not loopback (localhost, 127.0.0.0/8, ::1) unless you pass insecure_http=True: the bearer token and your code would otherwise cross the network unencrypted.
• The request, before it is sent, with the daemon's own limits: code size, step count and length, file count, project size, safe relative paths (no .., no leading /, no empty segment, no backslash, no control character), module table shape and result budget, a floor that is a real tier, and a software rule that is well formed. The trace ID (an opaque correlation ID the daemon writes on the run's audit line) must be 1 to 64 characters of [A-Za-z0-9._:-]: the daemon drops any other value without telling the caller, so the client refuses it instead.
• The protocol number. Every request states the number this client speaks (PROTOCOL); a daemon on another number refuses it before reading the payload. describe() compares the daemon's number with it and raises ProtocolMismatchError (with the description attached as info) when they differ.
• Every run record. The client recomputes the request digest from the JSON it sent and the result digest from the JSON it received, and checks the record's version, its provider, tier, environment and selected software against the answer, its software rule against the request, and its own digest. A single run's record must carry no session fields.
• The isolation evidence. The floor is sent with the request, so the daemon refuses before dispatch when its tier is below it; the tier the answer states is then checked against the floor again.
• A session's chain. Each call's record must name the session's fingerprint (the SHA-256 of the session ID), the next call number and the previous record's digest. At close, the daemon's count of executed calls and its last record must match what the client saw. A gap means someone else holding the session ID made a call. A call that may have run but ended in an error comes with its record (PlimsollError.unanswered, a version 3 record); the session checks it (its tier against the call's floor, and its provider, tier and software against what the session stated at open), hands it back as PlimsollError.record, keeps it in its chain and goes on. A call whose answer never arrived carries none, and neither does one cut short any other way (an answer this client cannot read, a KeyboardInterrupt), so the session refuses every later call before sending it, marked not dispatched: open a new one. Leaving a with block on an exception closes the session without hiding that exception behind the close's.
• The response size and the time. An answer over 32 MiB is refused, and request_timeout (default 360 seconds, above the daemon's five-minute ceiling on a run) bounds the whole HTTP exchange, not each socket read. Redirects are never followed and proxy settings in the environment are not used.

What each error means

Every error is a PlimsollError. The question that decides a retry is whether anything ran:

• err.not_dispatched is set (to request, permission, protocol, unsupported, isolation, environment, capacity or unknown) only when the daemon stated that nothing ran, or when the client refused the request before sending it. Sending the same request again, here or to another daemon, cannot run it twice.
• err.not_dispatched is None means the run may have executed, whatever the class or code. It is never a safe automatic retry of a request that is not idempotent.

Refusals. The class comes from the status code and the reason; the daemon marks these refusals, but read not_dispatched rather than the class, since a daemon that predates a procedure (sessions, for one) answers it unimplemented without the mark:

A plain PlimsollError carries any other Connect status in code (for example unauthenticated), marked or not as the daemon sent it.

Answered, but the answer does not check (DataLossError, never marked; the run may have executed, and err.result holds what came back):

No usable answer (TransportError, never marked): the connection failed, RequestTimeoutError (the exchange outlived request_timeout), ResponseTooLargeError (over 32 MiB), or MalformedResponseError (not a well-formed message of the expected type).

Stopped by a CancelHandle (RequestCanceledError, code canceled; not asyncio's CancelledError): marked not dispatched, reason request, when no byte of the request had been sent; unmarked once it may have been, since the daemon may have run it.

Limits

• NaN in module outputs. JSON writes every NaN (the floating-point "not a number" value) as the string "NaN", which loses the bits a NaN can carry. The daemon sends every NaN of a module output as the quiet NaN with no sign or payload, the one float("nan") encodes to, so the record checks whichever NaN the simulator produced; a NaN's sign and payload do not reach the client.
• Text files only. A project file's content is a protobuf string, so it must be text (str); captured artifacts come back as bytes.
• No signing. The Go module's attest package signs checked records outside the daemon; this client checks records and does not sign or store them.

Tests

go test ./clients/python serves the real daemon handler (the wasm provider for single runs, an in-memory session provider for sessions, and test handlers that tamper with or misstate answers) and runs the whole Python suite against it, with a fixture of digests the Go record package computed. It needs python3 3.10 or later and no network. The unit tests alone:

cd clients/python
PYTHONPATH=src python3 -m unittest discover -s tests -t .

The framework tools have a suite each in frameworks/<name>/, run by go test ./clients/python -run TestPythonFrameworks in a virtual environment per framework, at the version frameworks/<name>/requirements.txt pins: make py-frameworks builds them under tmp/py-frameworks/ (the first build downloads the frameworks; nothing calls a model or a paid service). The suites call each tool through its framework's own tool-call path (Agno's FunctionCall, CrewAI's run and arun), with no model and no agent loop, against the real daemon handler; make clients-suite runs them with every other client suite. The cancellation cases hold the daemon's Describe or a Run until released, cancel the await, and count the Run requests that reach the handler.