sift

Runs your command, then gives the model only the lines that matter.

A test suite prints 4,000 lines and eleven of them are the failure. A build prints a progress bar that redraws 900 times. An install lists every package it touched. All of it lands in the context window, and — this is the part that costs — it is re-sent in full on every turn that follows.

sift is an MCP server and a command line for that problem. It runs the command itself, keeps every byte on disk, and hands the model a view: the failures, the summary, the lines a reader would actually stop on. The rest is marked, not deleted.

Two numbers, both measured, both reproducible from this repository. Running this project's own test suite prints 652 lines — 21,392 tokens, as the model's own tokenizer counts them. What comes back is 8 lines and 208 tokens: 99% fewer (python test/kazanc.py). Removing almost everything is the easy half. Over a 22-sample corpus of real build and test output, the default budget keeps 138 of the 140 lines a reader could not do without (python test/budget.py).

$ sift run -- pytest
FAILED test/test_auth.py::test_expired_token - assert 401 == 200
  ...
─ 3,914 lines not shown · sift peek 9f2c41ab for any of them ─
=== 1 failed, 212 passed in 18.4s ===

A file you did not produce — a log, a saved CI transcript, a crash dump — gets the same treatment without being run:

$ sift digest ci-run-8812.log
2026-09-02T04:11:07 Building 214 targets
─ 38,904 lines not shown · sift peek ci-run-8812.log for any of them ─
ERROR: //src/parser:parse_test failed in 4.1s
─ 1,022 lines not shown · sift peek ci-run-8812.log for any of them ─
FAILED: 1 of 214 targets

A list is not read in lines. A JSON array written for a machine often has no newlines at all, and there is nothing in a line of one worth choosing, so the record becomes the unit and the same rules hold:

$ sift digest export.json
{"id": 3, "status": "failed", "error": "connection refused"}
─ 412 records not shown · sift peek export.json for the text they came from ─
{"id": 416, "status": "ok"}

The same question, asked about source code instead, is a table of contents:

$ sift outline src/parser.rs
pub struct Parser {
pub fn parse(input: &str) -> Result<Ast, Error> {
─ 34 lines not shown · sift peek src/parser.rs for any of them ─
impl Iterator for Tokens {

And a command that does not end — a dev server, a log tail, a build you want to keep working during — is started and then read a slice at a time:

$ sift run --background -- cargo build --release
9f2c41ab
$ sift follow 9f2c41ab
   warning: unused import: `std::fmt`
─ 212 lines not shown · sift peek 9f2c41ab for any of them ─
   error[E0308]: mismatched types
sift 9f2c41ab · running · new lines 1-247 · 2 shown · nemotron
$ sift follow 9f2c41ab          # only what has arrived since
$ sift follow --all --wait 30   # every run at once, holding for something new
$ sift stop 9f2c41ab            # ends it, and everything it started

Nothing is shown twice, and the numbers are the run's own: line 247 stays line 247 in sift peek for as long as the capture exists.

What decides

A free model does. sift sends it the numbered lines and asks one question: which numbers matter? It answers with numbers, and nothing else it says is used — the text you read above is printed from the local capture, byte for byte.

That is the whole trick, and it is why this is not a summariser. A summariser can be wrong about what a line said. sift cannot be: it never writes a line, it only chooses one.

It also means language coverage is not a list. A model reads Turkish, Japanese, Arabic and Hindi; it reads Rust, COBOL, Mojo and a language released last week. Nothing here enumerates them, so nothing here can be missing one.

Three rules

Nothing shown is invented. The judge returns line numbers. Text always comes from the local file.

Nothing is thrown away. sift peek <handle> returns the raw capture, unchanged. Every gap in a view says how many lines it covers.

Nothing can break your command. No API key, no network, an overloaded endpoint, a nonsense reply, a bug in the distiller, or a decision that nothing may leave this machine — every one of these falls back to rules that need none of them. The command still runs; you still get its output; you get its exit code.

What leaves the machine

One thing: the text of a question. Before it is sent, anything credential-shaped is replaced — tokens with a known prefix, JWTs, authorization headers, passwords in connection strings, the body of a PEM block.

That costs you nothing to read. The model is only ever asked for line numbers, and the lines are printed from your own file, so a line masked on the way out is still shown to you in full.

Three switches:

SIFT_MAX_CAPTURE=0  # keep everything a command writes, however much that is
SIFT_BASE_URL=... # ask your own endpoint instead, and no key is wanted
SIFT_MODELS=a,b   # which models to ask there, best first
SIFT_NO_MODEL=1   # never send anything; use the deterministic view
SIFT_MASK=0       # send unmasked
SIFT_CACHE=0      # ask again, even about text already answered
SIFT_EFFORT=low   # let the model think less, and lose some of what matters
SIFT_PATIENCE=0   # one quick pass only; do not wait out a busy hour

Masking is not complete and does not claim to be: a bare secret shaped like nothing in particular gets through. SIFT_NO_MODEL is the one that guarantees.

The fourth is a measured trade and is off by default. Asked which lines matter in a 404-line build, the model writes about 900 tokens of reasoning to produce a twelve-token answer, and you wait 15 seconds for it. At SIFT_EFFORT=low the same question takes 2.4 seconds — and over the corpus it loses 7.8% of the lines a reader could not do without, in exactly the places this tool exists for: a mainframe job's return code, a crash loop's diagnosis. Speed is available; it is not the default, and the price is written down.

The third is about not paying twice. An answer already given for exactly these bytes and exactly this question is used again instead of bought again — and what is kept is the numbers, never the view, so the text is still rendered from your own file and the gap still names your own capture. A view that cost no request says (remembered) where it would otherwise name the model.

Captured bytes never leave $SIFT_HOME (~/.cache/sift by default). Nothing is uploaded, nothing is logged elsewhere, and removing a capture directory removes everything that was ever kept about it.

One capture keeps at most a gigabyte. That is far past any real build log and a few seconds of a command stuck in a loop, which is the case it exists for: nothing is thrown away, and the disk somebody else needs is not filled either. Reading never stops — a pipe nobody drains would stop the command, and that is the one thing this will not do — so the command finishes, its exit code is its own, and the footer says kept the first 1,073,741,824 bytes of it rather than letting you believe you have the whole run. SIFT_MAX_CAPTURE=0 turns the ceiling off for anyone who would rather have the disk.

They also never go away on their own. Nothing here sweeps, expires or tidies in the background: sift gc [DAYS] is the only thing that deletes a capture, and it deletes when you type it and not before. What it leaves is one line per handle — when it went and how big it was, never the command — so that a gap marker read a fortnight later gets "removed on the 8th" instead of the answer it would give for a handle you made up.

Commands

sift run [--timeout SECONDS] [--shell] [--background] [--cwd DIR]
         [--budget LINES] [--keep PATTERN] [--] COMMAND...
sift follow [HANDLE] [--all] [--wait N]
                          what a background run has said since you last looked
sift stop [HANDLE]        end it, and everything it started
sift outline PATH|-       what a file declares, without its bodies
sift digest PATH...|-     what is in files somebody else produced
sift peek HANDLE|PATH [FIRST] [LAST]
sift hook                 answer one shell-command event on stdin
sift mcp                  speak the protocol on stdin, for a client
sift tools                which dense tools this machine has
sift tool NAME [ARGS...]  run one of them, distilled
sift memory [TERM]        what has been run here before, and how it went
sift list [COUNT]         what is running, and what has been run
sift stats [COUNT]        what the shortening cost, and what it saved
sift gc [DAYS]            remove captures older than that, and say what went

A path of - reads standard input, which is the other way somebody else's output turns up:

$ journalctl -u nginx --since yesterday | sift digest -
Sep 08 04:11:07 nginx[2114]: worker process 2119 exited on signal 11
─ 8,204 lines not shown · sift peek 7c1a04e9 for any of them ─
Sep 09 01:02:55 nginx[2114]: signal 15 (SIGTERM) received, exiting

What arrives on a pipe has no path anybody could type again, so it is kept as a capture of its own and the gap marker names that instead. The second rule is why: a view that left lines out and pointed at a scratch file would be pointing at nothing by the time somebody read it.

Several paths given to digest are asked about at the same time, and --all follows every running command in one go. Both are the same idea: the waiting is the cost, so do it once. --wait N holds until a run actually says something instead of answering that nothing has happened yet.

sift hook is the way to catch the shell commands a client runs on its own, without a proxy: point the client's pre-tool hook at it and every shell command comes here first. Everything is routed — nothing here guesses which commands are worth catching, because a list of those is a list of tools in disguise and how much a command prints is not knowable before it runs. Routing everything costs nothing: a view of twelve lines is twelve lines. It fails open, so a bug in it leaves your shell exactly as it was, and SIFT_HOOK=0 switches it off.

It is the part of this that pays most and the only part you have to turn on, so it offers itself rather than waiting to be found:

sift hook --install      # says what it gives and what it costs, then asks
sift hook --uninstall    # and takes it back out

It writes one line into your client's settings, keeps a copy of the file as it was, and touches nothing else that is in there. sift run mentions it once, ever, and then stops.

sift tool runs one of three programs that answer a question without opening the file — sg (ast-grep) for structural search, diff (difftastic) for a diff that can tell a reindent from a change, loc (scc) for the size of a tree. Their output is large by nature, which is exactly why they belong here. No binaries ship with this package: sift tools says which of them this machine has and what each is called, and installing one stays your decision.

sift memory asks no model at all. The question is counting — how often, how it went, which command has never once worked here — and a model asked to count is slower, costs a request and is sometimes wrong. The model decides what cannot be computed, and nothing else.

sift stats says what the shortening saved and what it cost, and keeps those two apart: the share is this tool's own arithmetic over bytes it holds, so it is exact, while the cost is the endpoint's count of its own tokens, so it is measured. A run the endpoint did not count is left out and said so, rather than filled in with bytes divided by four.

--keep PATTERN shows every line matching it whatever else was chosen and whatever the budget says. It is your pattern, not one this tool guessed at — the only place a pattern decides anything here, and it decides nothing until you type it. --budget LINES is the ceiling for one view.

In an agent

The same answers are available over MCP, and that is where they pay most: a tool result is re-sent on every turn that follows it, so a build log kept out of a transcript goes on staying out of it.

uv tool install "sift-cli[mcp]"   # or pipx; see Installing
claude mcp add --scope user sift -- sift-mcp

The key is read from ~/.config/nvidia/api_key, so it does not have to be in the environment and does not have to be pasted anywhere. --scope user puts the server in every project rather than the one you happen to be in.

Then restart the client. MCP servers are connected when a session starts, so the session you ran that command in will not see this one.

Without a key the server starts and every tool that would need a model declines with an explanation, so the agent falls back to its own shell rather than being handed a worse answer it cannot tell apart from a good one.

Any client that speaks stdio will do. The command is sift-mcp, and sift mcp starts the same server — one word for a client that would rather run the package by its own name (uvx --from "sift-cli[mcp]" sift-cli mcp, which is what the MCP registry entry says). It offers run, follow, outline, digest, digest_many, tool and peek. list and stats are deliberately not offered: they would hand a model every command lately run on this machine, including the ones it never asked about, and the person at a terminal already has that access while a model connecting over a socket does not.

Because a client never sees stderr, the last line of every result says what you are looking at: which handle, how the command ended, and whether a model chose the lines or none could be reached.

Installing

uv tool install sift-cli            # the command line, no dependencies at all
uv tool install "sift-cli[mcp]"     # and the MCP server

pipx install does the same thing. Either puts sift and sift-mcp on your PATH in an environment of their own, which is what you want for a command-line tool: nothing here belongs in the Python you build with.

Plain pip install sift-cli works inside a virtualenv you have already activated. It does not work against the system Python on Debian, Ubuntu, or WSL — those ship a EXTERNALLY-MANAGED marker and pip refuses, by design:

error: externally-managed-environment
× This environment is externally managed

That refusal is right and the answer is not --break-system-packages. Use uv tool or pipx.

The package is sift-cli and the commands are sift and sift-mcp. The names differ because sift-mcp on PyPI belongs to somebody else's project — an unrelated MCP server about authorising agent actions. Nothing here is theirs and nothing there is this.

Python 3.12 or newer, and no dependencies for the command line.

You need a model — a key, or one of your own

sift asks a model which lines matter. There are two ways to give it one and you need exactly one of them.

A free key

Not shipped, and not shareable. The key has to be yours. It is free, and it takes a minute:

1. Get a key at https://build.nvidia.com

2. Put it anywhere sift looks:

export SIFT_API_KEY=nvapi-...            # or NVIDIA_API_KEY
# or, once and for good:
mkdir -p ~/.config/nvidia && echo 'nvapi-...' > ~/.config/nvidia/api_key

Or a model of your own, and no key at all

Point sift somewhere and it asks there instead. Nothing about the question changes; the endpoint is asked the ordinary OpenAI-shaped way, and no Authorization header is sent when there is no key to put in it.

export SIFT_BASE_URL=http://localhost:11434/v1   # Ollama
export SIFT_MODELS=qwen3:8b                      # what to ask, best first

The same two lines fit llama.cpp (--api), vLLM, LM Studio, LocalAI, a company gateway, or any other endpoint that speaks POST /v1/chat/completions. SIFT_MODELS takes a comma-separated ladder and is asked in order.

An address you typed is treated as a decision: nothing warns you about a missing key, and the MCP server does not decline. What that endpoint wants for credentials is between you and it.

Tested here as a shape rather than as a list: the suite proves that an endpoint of your own is asked, and asked without a key. Which local servers answer well is a question about the model you run, and the corpus in test/budget.py is how you can settle it for yours.

Without either of them

The two callers are answered differently, on purpose:

• At a terminal everything still runs — the command, the bytes, the exit code, the third rule — and a loud banner says no model chose these lines and that you are looking at the ends of the output.

• Over MCP the tools decline and say why, and tell the agent to use its own shell instead. A person can see a degraded view and judge it; a model is handed a short text with a footer it has no reason to distrust, and quietly worse is the one thing this will not do to a reader who cannot check.

If you want to run without a model, say so with SIFT_NO_MODEL=1. That is a decision rather than an oversight, everything works, and nothing lectures you.

How it was built

Twenty-four phases, each one closed before the next began, each with a note in notlar/ saying what was decided and what it cost. notlar/00-PLAN.md is the arc, including the things that were deliberately not built and why.

The tests are in test/. Beside them is test/mutations.py, which breaks each rule the code follows — 162 of them, one at a time — and checks that the suite notices. A green suite says the tests did not object to this version of the code, not that they would object to a worse one.

It also says what happens when that battery is interrupted, because it was: a break left on disk survived every ordinary test run and took the machine down six times before anybody looked. test/conftest.py repairs one now, and the rule it was breaking is kept twice over, so that no single edit anywhere can turn sift stop into a signal to everything you own. That is notlar/19.

License

MIT.