principle-no-lookahead SKILL.md skillA
principle-no-lookahead from edbertchan/catstack is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add edbertchan/catstack/principle-no-lookahead@git:20260909.c3c9414Pins git:20260909.c3c9414 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- edbertchan/catstack
- Path
corpus/skills/principle-no-lookahead/SKILL.md- Versions recorded
- 1
- Latest version
- git:20260909.c3c9414, committed Sep 9, 2026
- Size
- 7,792 bytes
- Repository stars
- 6
- License
- none declared
Apply to any evaluation, backtest, benchmark, grader, or training run over data with a time axis or an ordered decision sequence. Score a decision only against inputs that existed before that decision was made. Covers what the field calls look-ahead bias, target leakage, point-in-time correctness, and repainting. Reach for it on: a backtest or walk-forward run, a feature computed over a full history, a retrieval or agent eval, a label assigned after the outcome was known, or any result that…
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# No lookahead A result is a result only if the decision behind it could have been made at the moment it is credited to. Otherwise it is a measurement of hindsight. The failure has a formal name: **leakage** — "the introduction of information about the target of a data mining problem which should not be legitimately available to mine from" (Kaufman et al., see Grounding). In time-series work it is **look-ahead bias**; the correctness property it violates is **point-in-time correctness**; the technical-analysis artifact that causes it is a **repainting** indicator. One defect, four vocabularies. ## The shape Two artifacts get confused because they are rendered from the same data: | | Display artifact | Decision artifact | |---|---|---| | Answers | what happened | what would I have done | | May read | the whole history | only rows at or before `t` | | Revised later | legitimately, yes | never | A chart, a labelled dataset, an annotated log, a resolved ticket, and a post-hoc report are all display artifacts. They are drawn *after*, and are allowed to move a marker back onto the moment the thing "really" happened. …
Read the whole file at its exact version.
How to install
mdr add edbertchan/catstack/principle-no-lookahead@sha256:7bffc3039619dbc4The line at the top of this page pins the label git:20260909.c3c9414, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_siblojz7ofznng3y)
2 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 1 version of this file, committed on Sep 9, 2026.
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (7792 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
edbertchan/catstack · 6 stars · license none declared · pushed 2026-10-22 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_siblojz7ofznng3y GET https://markdownregistry.com/api/v1/resolve?ref=edbertchan/catstack/principle-no-lookahead GET https://markdownregistry.com/api/v1/blob/7bffc3039619dbc4e953ec951f919b59dc5fb8fa41aec546118684ee56b3cf3b
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.