agent-walkforward

Stop overfitting your agent to its eval set.

Agent eval tools (agentevals, RAGAS, DeepEval, your own JSONL log) score your agent against a fixed set of cases. You tweak a prompt, the score goes up, you ship. Sound familiar? It's the same trap quants fell into for decades: tune a strategy against one slice of history, the backtest looks great, live trading falls apart. The score went up because you overfit the test, not because the agent got better.

agent-walkforward borrows the fix quants already built — walk-forward validation with purge and embargo — and applies it to eval logs. It splits your time-ordered eval records into in-sample (IS) and out-of-sample (OOS) folds, then measures how much the score degrades out-of-sample. A large, persistent IS→OOS gap means your gains are overfit to the eval set.

• Zero dependencies. Pure standard library. pip install and go.
• Bring your own eval tool. Reads JSONL / JSON / CSV with configurable field names — it sits on top of whatever you already use, not instead of it.
• Leakage-aware. Purge (drop IS records sharing a session/group with OOS) and embargo (temporal buffer) prevent the split from lying to you.

Install

pip install agent-walkforward

Or from source:

git clone https://github.com/Starlight143/agent-walkforward
cd agent-walkforward
pip install -e ".[dev]"

Quickstart

Your eval log is a list of scored records, ordered in time (by run, by version, by commit — anything monotonic). One record per line for JSONL:

{"id": "case-001", "timestamp": 1, "score": 0.92, "group": "sessionA"}
{"id": "case-002", "timestamp": 2, "score": 0.88, "group": "sessionA"}

Run it:

agent-walkforward run --traces examples/sample_traces.jsonl --n-splits 4 --oos-size 8

agent-walkforward 0.1.0  |  records=50
fold  IS_n  OOS_n   IS_mean  OOS_mean      gap   degr  purged  embargo
   1    18      8    0.886    0.787    0.099   0.889       0        0
   2    26      8    0.856    0.729    0.127   0.851       0        0
   3    34      8    0.826    0.670    0.156   0.811       0        0
   4    42      8    0.796    0.608    0.189   0.763       0        0
------------------------------------------------------------------
overall IS_mean= 0.841  OOS_mean= 0.698  mean_gap= 0.143
VERDICT: OVERFIT_RISK

The OOS score sits well below IS and the gap widens fold over fold — a textbook sign that improvements are being tuned into the eval set rather than into the agent.

As a library

from agent_walkforward import load_records, walk_forward_splits, evaluate

records = load_records("evals.jsonl")
sorted_records, folds = walk_forward_splits(records, n_splits=4, oos_size=8, embargo=2)
report = evaluate(sorted_records, folds)

print(report.verdict, report.mean_gap)
for f in report.folds:
    print(f.index, f.is_mean, f.oos_mean, f.gap)

Concepts

Term	What it means here
In-sample (IS)	Records you'd have tuned against — everything before an OOS block.
Out-of-sample (OOS)	A held-out block of later records the tuning never saw.
Walk-forward	Consecutive OOS blocks tile the tail of the series; IS expands (or rolls) up to each block.
Purge	Drop IS records whose group (session / conversation / seed) also appears in the OOS block, so a shared context can't leak across the boundary.
Embargo	Drop the N IS records immediately before an OOS block, a buffer against temporal spillover.
Gap	IS_mean − OOS_mean. Positive and growing ⇒ overfitting.
Degradation	OOS_mean / IS_mean (only meaningful for non-negative scores).

Interop

The loader maps whatever field names your tool emits:

agent-walkforward run --traces run.csv \
  --id-field case_id --time-field ts --score-field response_match_score \
  --group-field conversation_id

That makes it a drop-in post-processor for agentevals OTel exports, RAGAS result tables, DeepEval logs, or a hand-rolled JSONL.

Agent integrations

Built to be called by coding agents (Claude Code, Cursor, Cline, ...), three ways:

1. One-call Python API — returns a plain JSON-serializable dict:

from agent_walkforward import analyze

result = analyze("evals.jsonl", n_splits=5, oos_size=10, embargo=2)
# also accepts a list of dicts or EvalRecord objects instead of a path
print(result["verdict"], result["mean_gap"])

2. CLI with --json — for agents that shell out and parse stdout:

agent-walkforward run --traces evals.jsonl --json

3. MCP server — expose it as a native tool to any MCP client:

pip install "agent-walkforward[mcp]"
agent-walkforward-mcp          # stdio transport

Example Claude Desktop / Cursor config:

{
  "mcpServers": {
    "agent-walkforward": { "command": "agent-walkforward-mcp" }
  }
}

The server exposes one tool, walkforward_analyze, taking either a traces_path or inline records.

Claude Code skill — a ready-made skill lives in integrations/claude-code-skill/. Copy it to ~/.claude/skills/agent-walkforward/ and Claude Code will reach for it whenever you ask "are these eval gains real or overfit?".

When this helps — and when it doesn't

Walk-forward assumes your eval records have temporal / versioned order and that you iterate against them over time. It shines when you have a growing eval log across many runs or agent versions.

It does not help a one-shot eval of a static set with no ordering — there's no "later" to hold out. And the verdict is a heuristic on the score scale (default tuned for 0–1 scores), not a statistical significance test. Treat it as a smoke alarm, not a p-value.

Development

pip install -e ".[dev]"
pytest -q

License

MIT — see LICENSE.