contexel 0.1.13

Deterministic, dependency-free context-economy stages for code-writing agents.

The context element. Deterministic, dependency-free context shaping for code-writing agents — the same transform, every run.

Why this exists

An agent's tools return big lists of records: search hits, file reads, API responses. Before they reach the model's context window they must be cut down — and today that cutting is usually code the model improvises fresh each run, which drifts: different field choices, different truncation, different survivors, every time. contexel replaces the improvisation with vetted, versioned stages at the tool → context boundary. Same input, byte-identical context, on every run — a context contract instead of a nightly rewrite.

What you get

Six deterministic pipeline stages plus a merge combiner, over plain list[dict] — the shape tools already return — with composition and observability:

• select — project to the fields you need (lossless)
• dedupe — drop duplicates by key, type-qualified, order preserved (lossless)
• rescore — BM25-style lexical relevance derived from the records' own text, so ranking doesn't have to trust the tool's score
• rank — stable sort, missing-field records last
• truncate_field — clip a text field to a token cap, never exceeding it
• trim_to_budget — keep the top records that fit a token budget
• merge — unify differently-shaped tool outputs into one schema
• pipeline([...]) / @shaped / trace() — compose, pin at the tool boundary, and inspect what every stage removed

Token counting is pluggable twice over: the tokenizer (a dependency-free estimate by default; tokens.use_tiktoken() for exact) and the serializer (budgets are priced in the encoding your boundary actually emits — JSON by default, or e.g. an ISON table).

No embeddings, no model calls, zero dependencies — pure Python 3.9+.

Install

pip install contexel              # pure Python, zero dependencies
pip install "contexel[accurate]"  # + tiktoken, for exact token counts

Sixty seconds

from contexel import select, dedupe, rescore, truncate_field, rank, trim_to_budget, trace

raw = search_tool(query=user_query)          # a batch of verbose results

with trace() as t:
    r = select(raw, ["title", "url", "snippet", "published"])
    r = dedupe(r, key="url")
    r = rescore(r, query=user_query, fields=("title", "snippet"))
    r = truncate_field(r, "snippet", max_tokens=120)
    r = rank(r, by="score", desc=True)
    r = trim_to_budget(r, max_tokens=1500)

print(t.report())    # per-stage: records in -> out, tokens before -> after
context = r          # only this distilled result enters the model's context

Or pin the policy at the tool boundary, so the model never sees raw output:

from contexel import shaped, stage, select, dedupe, trim_to_budget

@shaped([
    stage(select, fields=["path", "line", "snippet"]),
    stage(dedupe, key=["path", "line"]),
    stage(trim_to_budget, max_tokens=2000),
])
def search_code(query: str) -> list[dict]:
    return repo.search(query)     # shaped identically, every call

Measured, not asserted

Benchmarked on the full CodeSearchNet python/test split (22,176 real functions → 28,047 search-tool records) with 100 ground-truth episodes: contexel is the only implementation among the near-neighbours (hand-written glue, toolz, langchain-core, llama-index-core) that covers all the operations natively, holds a 1,500-token budget in 100% of episodes, keeps the needed record in 100% of them under both a strong and a weak retrieval signal, and spends 100% of context tokens on unique, needed fields — at 0 dependencies and a 13 ms import. It is also the slowest budget-compliant row, because it does the most work per record — and the limits are stated with the same care: recall@budget is bounded by query specificity for any shaper, and rescore is lexical, not semantic.

Determinism is proven, not promised: the suite hashes the same contract's output across fresh interpreters with different PYTHONHASHSEED values — same SHA-256 every time, even when raw tool output carries fresh request ids.

Full method and tables: benchmarks/COMPARISON.md · benchmarks/RESULTS.md

Where it fits

Inside agent-written code (programmatic tool calling), as a @shaped tool wrapper, inside an MCP server, under LangChain/LlamaIndex via a thin adapter, or ahead of a token-efficient encoding — each with a runnable example in examples/, plus a complete no-API-key reference agent (python -m reference_agent).

Links

• Docs: https://maheshvaikri-code.github.io/contexel/
• Source: https://github.com/maheshvaikri-code/contexel
• Changelog: https://github.com/maheshvaikri-code/contexel/blob/main/CHANGELOG.md
• License: MIT