ctxopt

A lightweight CLI for taming LLM context windows.

ctxopt helps you keep conversations with LLMs — and the agents built on them — lean. It does three things, each independently useful:

• 🧹 Sandbox noisy tool output (logs, stack traces, diffs, JSON blobs) down to a compact form that fits an actual token budget, instead of dumping thousands of lines into your context.
• 📝 Summarize long conversations or transcripts into a shorter digest, locally and deterministically — no API calls required.
• 🧭 Route a prompt to the right model tier based on an estimate of how complex it actually is, so you're not paying frontier-model prices for "what's the capital of France?"

No heavy dependencies, no required API keys, no telemetry. It's a small tool that does a small number of things well.

Install

pip install ctxopt

Or from source:

git clone https://github.com/feralxr/ctxopt.git
cd ctxopt
pip install -e .

Requires Python 3.9+.

Usage

Sandbox noisy output

This is the core command: it collapses long, repetitive, or oversized tool output while preserving the signal that actually matters.

ctxopt sandbox build.log
# or pipe it in:
cat build.log | ctxopt sandbox

Token-budget fitting (recommended — tokens, not lines, are what fill a context window):

ctxopt sandbox giant_stacktrace.log --max-tokens 300

  File "app.py", line 14, in recurse
    return recurse(n-1)
RecursionError: maximum recursion depth exceeded
profile=stacktrace  5346 -> 118 tokens (5228 saved, 981 lines elided, fit to budget)

Near-duplicate collapsing. Lines that are identical after stripping volatile bits (timestamps, hex addresses, UUIDs, standalone counters) get folded together — this is what actually tames recursive stack traces and progress spam, where only a counter or timestamp changes line to line. Digits embedded inside an identifier (like line1 or v2) are left alone, so distinct content never silently merges:

ctxopt sandbox big_diff.patch

diff --git a/big_module.py b/big_module.py
--- a/big_module.py
+++ b/big_module.py
@@ -1,300 +1,300 @@
+added line 0
... [299 near-identical line(s) collapsed] ...
profile=diff  1216 -> 28 tokens (1188 saved, 0 lines elided)

Content profiles. ctxopt sandbox auto-detects the shape of the input (--profile auto by default) and adjusts behavior accordingly:

JSON example — a 300-user payload with 800-character bios collapses to a fraction of its size while staying parseable:

ctxopt sandbox users.json

{
  "users": [
    { "id": 0, "name": "user_0", "bio": "xxxx...xx... [300 chars truncated]" },
    ...
  ]
}

profile=json  2401 -> 306 tokens (2095 saved, 0 lines elided)

Signal preservation. Lines matching error, exception, fail(ed/ure), traceback, fatal, or panic are never elided, even inside the collapsed middle — up to a cap (max_kept_matches as a library param) so a pathological log full of "error" lines can't defeat the budget. Add your own patterns with --keep:

ctxopt sandbox app.log --keep "payment_id=\w+" --max-tokens 500

Flags:

Summarize a conversation

This is conversation-aware, not just a document shortener. It detects two transcript formats — Role: message plain text, and JSON message lists ([{"role": ..., "content": ...}], the shape most chat APIs use) — and summarizes turn by turn. Anything else falls back to paragraph-based segmentation.

ctxopt summarize support_thread.txt --max-tokens 120

A 47-turn transcript — a real bug report, 39 repetitive "any update?" check-ins, and a resolution — collapses to the parts that matter:

User: Hey, the deploy script is failing on staging.

Assistant: Can you share the error output?

User: Sure, here it is: ValueError: missing config key DATABASE_URL

Assistant: Looks like the staging .env file is missing that key. I will check.

Assistant: still looking into it, item 10 is in progress.

Assistant: Found it, the key was renamed in the last config migration. We
decided to add a fallback default for it.

User: Perfect, that fixed it. Thanks!

Assistant: Glad it works now. Let me know if anything else comes up.

backend=local  640 -> 120 tokens  turns 8/47

The problem report, the diagnosis, the decision, and the resolution all survived; the 39 near-identical "checking in" turns didn't.

How segments are chosen, same philosophy as sandbox's keep patterns:

• Lines matching error, exception, decided, or important are always kept, plus any --keep <regex> you add, however small the budget.
• The most recent --keep-last turns (default 2) are always kept — only meaningful for conversations, ignored for plain documents.
• Everything else is scored by length, keyword density, and position, then greedily added until the budget is met — skipping any candidate that's a near-duplicate (word-overlap above redundancy_threshold) of something already kept, so repetitive check-ins don't all survive just because each one scores decently on its own.

This local mode is fully offline and deterministic — no network calls, no cost, same input always gives the same output.

Abstractive summaries (optional). Pass --llm to use a real model instead of the local heuristic. It reads ANTHROPIC_API_KEY from your environment and does a small map-reduce: segments are grouped into token-sized chunks, each chunk gets summarized by the model, and — only if the combined chunk summaries still exceed the target — one final call reduces them into a single digest.

export ANTHROPIC_API_KEY=sk-...
ctxopt summarize huge_transcript.txt --llm --max-tokens 300

As a library, llm_call is just Callable[[str], str] — point it at anything, not just Anthropic:

from ctxopt import summarize_text, anthropic_backend

result = summarize_text(transcript, llm_call=anthropic_backend(), max_tokens=300)
print(result.backend, result.text)  # "llm", "..."

Route a prompt to a model tier

Score a prompt's complexity and get a model recommendation back:

ctxopt route "What is the capital of France?"

Score    0.00
Tier     simple
Model    claude-haiku-5-5
Reasons  2 simple-query keyword(s) matched

ctxopt route "Design a fault-tolerant distributed architecture for this payment system and debug the race condition below: ..."

Score    0.74
Tier     complex
Model    claude-opus-5-5
Reasons  contains code or code-like syntax; 4 complexity keyword(s) matched

The scoring heuristic weighs input length, presence of code, and complexity/simplicity keyword signals. Tiers and model names are fully configurable — see below.

Using it as a library

Every command is backed by a plain Python function with no CLI coupling:

from ctxopt import sandbox_text, summarize_text, route, RouterConfig

# Collapse noisy output to fit an actual token budget
result = sandbox_text(log_text, max_tokens=500)
print(result.profile, result.text, result.original_tokens, result.final_tokens)

# Always preserve your own markers (e.g. a request/trace id), on top of the
# built-in error/exception/fail defaults
result = sandbox_text(log_text, max_tokens=500, keep_patterns=[r"trace_id=\w+"])

# Summarize a transcript (conversation-aware, local and free)
digest = summarize_text(transcript_text, max_tokens=300, keep_last_n_turns=3)
print(digest.turns_kept, "of", digest.turns_total, "turns kept")

# Route to a model tier, with your own model names
config = RouterConfig(tiers={
    "simple": "gpt-4o-mini",
    "standard": "gpt-4o",
    "complex": "o1",
})
decision = route(user_prompt, config)
print(decision.tier, decision.model, decision.reasons)

Why this exists

Agent and chat pipelines accumulate context fast: verbose tool output, sprawling multi-turn history, and routing every request — simple or complex — through the same expensive model. ctxopt is a small set of composable primitives for the three most common sources of that bloat. It's not a framework and doesn't ask you to adopt an architecture — pipe things in, get leaner things out.

Development

git clone https://github.com/feralxr/ctxopt.git
cd ctxopt
pip install -e ".[dev]"
pytest

Every push/PR to main runs the test suite across Python 3.9–3.12 via .github/workflows/tests.yml.

Publishing

Releases are published to PyPI via Trusted Publishing (OIDC) — no PyPI API token is ever stored as a secret. One-time setup on PyPI's side, under Your project → Publishing → Add a new pending publisher:

After that's linked, cutting a release is just:

# bump the version in pyproject.toml and src/ctxopt/__init__.py first
git tag v0.2.0
git push origin v0.2.0

.github/workflows/workflow.yml builds the sdist/wheel, checks the tag matches pyproject.toml's version, and publishes.

License

MIT — see LICENSE.