ctxbudgeter 0.2.0

Context compiler for agentic AI: compile clean, cheap, auditable context under a token budget. Framework-agnostic. Local-first. Deterministic.

ctxbudgeter

Compile clean, cheap, auditable context for AI agents.

ctxbudgeter is a framework-agnostic context engineering toolkit for agentic AI. Hand it the raw materials — system rules, docs, code, memory notes, tool results, the latest user request — and it decides what enters the model, what gets dropped, what gets compressed, what should be cached, and why. Every decision is auditable. Every compilation is deterministic. Tests can gate on context the same way they gate on code.

Use any agent framework. ctxbudgeter sits in front of LangGraph, CrewAI, OpenAI Agents SDK, PydanticAI, Microsoft Agent Framework, or your own loop. It does one thing: make the context you send to the model cleaner, cheaper, and assertable.

Webpack for agent context  •  pytest for prompt/context quality  •  token budget manager

What you get

• Token budget compiler — deterministic, explainable selection with full inclusion/exclusion reasons
• Just-in-time References — lazy pointers (file paths, URLs, queries) that only load if they fit
• Eval / assert layer + pytest plugin — assert_includes, assert_health_at_least, golden snapshots
• Cache-aware adapters — Anthropic cache_control placement, OpenAI prompt_cache_key, LangChain & PydanticAI
• Multi-modal attachments — images and structured tool schemas flow through to OpenAI/Anthropic payloads
• Sensitivity enforcement — allow | warn | refuse | redact for items tagged secret
• Memory store (Write strategy) — persist agent notes between turns, query them back into context
• Isolation (Isolate strategy) — pack.fork() builds a subagent-scoped pack with its own budget
• Async compile — concurrent resolution of async References, async-aware compressor hook
• Declarative YAML/JSON specs — check pack configuration into git, CI-friendly
• CLI — scan, compile, pack, validate, report for Claude Code and CI workflows
• Zero LLM calls in the core — local-first, deterministic, fast

Install

pip install ctxbudgeter

# Optional extras
pip install "ctxbudgeter[tiktoken]"        # accurate OpenAI/Anthropic-proxy tokenization
pip install "ctxbudgeter[yaml]"            # YAML pack specs
pip install "ctxbudgeter[http]"            # http_get loader for References
pip install "ctxbudgeter[anthropic,openai,langchain]"
pip install "ctxbudgeter[all]"             # everything

Python 3.10+. Adapters are lazy-imported — you only pay for the SDKs you actually use.

Quick start

from ctxbudgeter import ContextPack

pack = ContextPack(
    model="claude-sonnet-4.6",
    token_budget=24_000,
    reserved_output_tokens=4_000,
)

pack.add(
    name="system_rules",
    content="You are a careful coding agent...",
    kind="system",
    priority=100,
    cache_policy="stable",
    required=True,
)
pack.add_file("README.md", kind="project_doc", priority=80)
pack.add(
    name="task",
    content="Build the referral packet UI.",
    kind="task",
    priority=95,
    required=True,
)

compiled = pack.compile()
print(compiled.report())

Included:
  - system_rules: 312 tokens, required, stable cache prefix, system
  - README.md: 1,420 tokens, stable cache prefix, project_doc
  - task: 19 tokens, required, task

Excluded:
  - old_notes.md: token-heavy and low priority — 8,400 tokens, score 41
  - debug.log: token-heavy and low priority — 14,200 tokens, score 12

Estimated input tokens: 1,751
Reserved output tokens: 4,000
Cacheable prefix: 1,732 tokens
Token budget: 24,000 (utilization 8.8%)
Context health score: 87/100
  breakdown: cacheable_prefix_bonus: +5, under_utilized: -5
Tokenizer: tiktoken

Just-in-time References

Don't load context you'll never use. References are lightweight pointers that load only when they could plausibly fit the budget — Anthropic's "JIT" pattern, built in.

from ctxbudgeter import ContextPack
from ctxbudgeter.loaders import file_loader, http_get_loader, register_loader

pack = ContextPack(token_budget=24_000)
pack.add(name="task", content="Refactor auth", kind="task", required=True)

# File reference — only opened if it would fit
pack.add_reference(
    name="auth_module",
    location="src/auth.py",
    loader=file_loader,
    estimated_tokens=1200,
    kind="code",
    priority=70,
)

# HTTP reference — never fetched unless budget allows
pack.add_reference(
    name="api_docs",
    location="https://example.com/docs/api.json",
    loader=http_get_loader,
    estimated_tokens=2000,
    kind="retrieval",
    priority=60,
)

# Or register your own loader
@register_loader("vector_search")
def vector_search(ref):
    return my_vector_store.search(ref.location, k=3)

pack.add_reference(name="docs_hit", location="referral packet UI", loader=vector_search, estimated_tokens=500)

compiled = pack.compile()

Async loaders work too — use await pack.acompile():

async def fetch_user_profile(ref):
    async with httpx.AsyncClient() as c:
        r = await c.get(ref.location)
        return r.text

pack.add_reference(name="profile", location="https://api.example.com/me", loader=fetch_user_profile, estimated_tokens=300)
compiled = await pack.acompile()   # async references resolved concurrently

Eval / assert layer — "pytest for prompts"

from ctxbudgeter.testing import (
    assert_includes, assert_excludes,
    assert_health_at_least, assert_cacheable_prefix_at_least,
    assert_no_secret_items, assert_used_tokens_at_most,
    GoldenPack,
)

def test_prod_pack():
    compiled = build_prod_pack().compile()
    assert_includes(compiled, "system_rules", "task")
    assert_excludes(compiled, "debug.log")
    assert_health_at_least(compiled, 80)
    assert_cacheable_prefix_at_least(compiled, 1024)
    assert_no_secret_items(compiled)
    assert_used_tokens_at_most(compiled, 20_000)

def test_pack_golden(ctxbudgeter_golden):
    # Provided by the installed pytest plugin.
    # Stores a golden snapshot the first time, diffs against it after.
    ctxbudgeter_golden().check(build_prod_pack().compile())

Refresh goldens after intentional changes:

pytest --ctxbudgeter-update-golden

Cache-aware adapters

from ctxbudgeter.adapters import (
    to_anthropic_request,  # cache_control on last stable system block
    to_openai_request,     # prompt_cache_key derived from stable prefix hash
    to_langchain_messages,
    to_pydantic_ai_deps,
)

# Anthropic
import anthropic
client = anthropic.Anthropic()
resp = client.messages.create(**to_anthropic_request(compiled, user_message="next step?"))

# OpenAI — explicit cache key for prompt-prefix caching
from openai import OpenAI
oa = OpenAI()
resp = oa.chat.completions.create(**to_openai_request(compiled, user_message="what now?"))

# LangChain
from langchain_anthropic import ChatAnthropic
msgs = to_langchain_messages(compiled, user_message="continue")
ChatAnthropic(model=compiled.model).invoke(msgs)

# PydanticAI
deps = to_pydantic_ai_deps(compiled)
agent.run(deps["system_prompt"], message_history=deps["message_history"])

Multi-modal attachments

from ctxbudgeter import ContextPack, ImageBlock, StructuredBlock

pack = ContextPack(token_budget=24_000)
pack.add(
    name="screenshot",
    content="Describe what's wrong in this screenshot.",
    kind="user_message",
    attachments=[
        ImageBlock(url="https://example.com/bug.png", estimated_tokens=400),
    ],
)
pack.add(
    name="tools",
    content="",
    kind="tool_def",
    cache_policy="stable",
    priority=85,
    attachments=[
        StructuredBlock(schema_name="search_db", data={"args": ["query"], "returns": "list[Doc]"}),
    ],
)

Image and structured blocks flow through to OpenAI's image_url / Anthropic's image / tool_result formats automatically.

Sensitivity enforcement

pack.add(name="api_key", content="sk-DEADBEEF...", sensitivity="secret")

pack.set_secret_policy("warn")     # include but flag in report + health penalty (default)
pack.set_secret_policy("refuse")   # raise SecretContentError at compile time
pack.set_secret_policy("redact")   # replace content with [REDACTED — sensitivity=secret]
pack.set_secret_policy("allow")    # silently allow (escape hatch)

In CI you almost always want refuse or redact. The text/markdown reports flag [!secret] items so reviewers can catch leaks during PR review.

Memory (Write strategy) + Isolation (Isolate strategy)

from ctxbudgeter import ContextPack, InMemoryStore, JSONMemoryStore, MemoryNote

# Persist notes across turns
store = JSONMemoryStore(".ctxbudgeter/memory.json")
store.write(MemoryNote(key="auth_runbook", content="JWT rotation...", tags=["auth"]))

# Pull them back into a future pack
pack = ContextPack(token_budget=24_000)
pack.add(name="task", content="Fix auth bug", required=True)
pack.add_memory(store, tags=["auth"], limit=3, priority=70)

# Isolate a subagent's context — only frontend code, smaller budget
frontend_pack = pack.subset_by_kind("project_doc", "code").fork(
    filter=lambda it: it.metadata.get("area") == "frontend",
    token_budget=8_000,
)

Declarative YAML pack specs

Check your pack into git like any other config:

# pack.yaml
model: claude-sonnet-4.6
token_budget: 24000
reserved_output_tokens: 4000
secret_policy: refuse

items:
  - name: system_rules
    from_file: prompts/system.md
    kind: system
    priority: 100
    required: true
    cache_policy: stable

  - name: task
    content: "Fix the auth bug."
    kind: task
    priority: 95
    required: true

references:
  - name: api_docs
    location: "https://example.com/docs.json"
    loader: http_get
    estimated_tokens: 1500
    priority: 60

Then compile from the CLI:

ctxbudgeter validate pack.yaml
ctxbudgeter pack pack.yaml --format markdown -o report.md
ctxbudgeter pack pack.yaml --fail-below 80    # exit non-zero on low health for CI

Or from Python:

from ctxbudgeter.spec import load_pack
pack = load_pack("pack.yaml")
compiled = pack.compile()

CLI

# Scan a directory, suggest priorities + cache policies
ctxbudgeter scan . --max-files 50

# Scan + emit a starter pack.yaml you can commit and iterate on
ctxbudgeter scan . --emit-pack pack.yaml --task "ship feature X"

# Ad-hoc compile from a directory + task
ctxbudgeter compile . --task "fix auth bug" --budget 12000 --secret-policy refuse

# Compile from a declarative spec
ctxbudgeter pack pack.yaml --format markdown -o context-report.md

# Re-render a saved compiled pack
ctxbudgeter compile . --task "..." --save-pack pack.json
ctxbudgeter report pack.json --format markdown

Wire it into CI

GitHub Actions

# .github/workflows/context-check.yml
name: Context budget check
on: [pull_request]

jobs:
  ctxbudget:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: "3.11"
      - run: pip install "ctxbudgeter[all]"
      - name: Validate and compile pack
        run: |
          ctxbudgeter validate pack.yaml
          ctxbudgeter pack pack.yaml --format markdown --fail-below 80 -o report.md
      - name: Comment report on PR
        uses: marocchino/sticky-pull-request-comment@v2
        with:
          path: report.md

pre-commit

# .pre-commit-config.yaml
repos:
  - repo: local
    hooks:
      - id: ctxbudgeter-validate
        name: ctxbudgeter validate pack.yaml
        entry: ctxbudgeter validate pack.yaml
        language: system
        pass_filenames: false
        files: ^pack\.yaml$

pytest

# tests/test_context.py
from ctxbudgeter.testing import (
    assert_health_at_least, assert_no_secret_items, assert_includes,
)
from my_app.context import build_pack

def test_production_pack_quality():
    compiled = build_pack(task="fix auth bug").compile()
    assert_includes(compiled, "system_rules", "task")
    assert_health_at_least(compiled, 80)
    assert_no_secret_items(compiled)

How it works

Compiler algorithm

1. Resolve References — load only those whose estimated cost could fit. Loader failures → excluded with reason.
2. Required items go in first; compress (via your hook) or truncate if they don't fit.
3. Optional items ranked by score_item, packed greedily.
4. Sensitivity policy applied (warn / refuse / redact / allow).
5. Final prompt order: stable → dynamic → ephemeral, deterministic tie-breaks.
6. Cacheable prefix = consecutive stable items at the top.

score = priority*0.5 + relevance*100*0.3 + freshness*100*0.1 + cache_value*100*0.1 - token_cost_penalty

token_cost_penalty grows up to ~30 points as an item approaches the full budget — a 50k-token debug log doesn't beat your README on priority alone.

Health score breakdown

A 0–100 score with explicit, auditable deductions. Each pack reports its breakdown:

{
  "health_score": 87,
  "health_breakdown": {
    "cacheable_prefix_bonus": 5,
    "under_utilized": -5,
    "high_priority_excluded": -10,
    "secrets_included": -10
  }
}

If you'd rather not show "health" — treat it as BudgetCheckScore: a determinstic, explainable signal, not a quality oracle.

Compression hook

ctxbudgeter never calls an LLM for you. Provide a function — sync or async, your choice:

async def my_summarizer(item, target_tokens):
    return await anthropic_client.summarize(item.content, max_tokens=target_tokens)

pack.set_compressor(my_summarizer)
compiled = await pack.acompile()   # async path; sync compressors also work with .compile()

If your compressor returns content larger than target_tokens, the compiler retries once with a tighter target before giving up.

Round-trip + tooling

import json
from ctxbudgeter import compiled_pack_from_dict

# Compile, save, share
compiled = pack.compile()
Path("compiled.json").write_text(json.dumps(compiled.to_dict()))

# Reload later for reporting / diffing / assertions
restored = compiled_pack_from_dict(json.loads(Path("compiled.json").read_text()))
print(restored.report("markdown"))

Positioning

Most agent frameworks ask: "which agent runs next?" ctxbudgeter asks: "what exact information should this agent see right now — and why?"

Layer	Existing	What ctxbudgeter adds
Agent frameworks	LangGraph, CrewAI, OpenAI Agents SDK, PydanticAI	Decides the context shape before the call
RAG	LlamaIndex, LangChain retrievers	Retrieval ≠ final context; ctxbudgeter is the gate
Observability	LangSmith, AgentOps	They show what happened after; we prevent before
Context tools	ctxforge, contextkit, contextagent	We're the assertable + deterministic option

Design choices

• Local-first. No LLM API calls in the core. The compiler is pure Python.
• Deterministic. Same inputs → identical compiled pack. Same JSON output. Same health score. Always.
• Explainable. Every input item shows up in decisions with a status and a human-readable reason.
• Framework-agnostic. Core has zero hard dependencies on agent SDKs. Adapters are lazy-imported.
• Composable. Bring your own tokenizer, your own compressor, your own scoring weights, your own loaders, your own memory store.
• Assertable. Quality gates live in pytest, not in your head.

Author

Karan Chandra Dey — [K28] Founder and AI Product Builder @ K28 Design Lab · k28art.space

Helping SMEs ship their first AI MVP — from prompt engineering to context engineering to production-ready agents.

Web	k28art.space
GitHub	@Kayariyan28
LinkedIn	karan-chandra-dey
Email	[e-mail]

"Use any agent framework. ctxbudgeter makes your context cleaner, cheaper, and assertable — before the model sees it."

License

MIT © Karan Chandra Dey / K28 Design Lab.