ds

name	ds
description	This skill should be used when the user asks to 'start data analysis', 'brainstorm analysis approach', 'plan a data project', 'clarify analysis requirements', 'explore this dataset', 'what's in this data', 'what should I analyze here', 'set up a new study', or needs the data science workflow (exploration starts with questions, not data pulls — the workflow enforces that ordering).
allowed-tools	Read, Grep, Glob, Bash, Skill, TodoWrite
hooks	{"PreToolUse":[{"matcher":"Bash","hooks":[{"type":"command","command":"uv run python3 ${CLAUDE_PLUGIN_ROOT}/hooks/ds-brainstorm-no-exploration-guard.py"}]}]}

Contents

• The Iron Law of DS Brainstorming
• What Brainstorm Does
• Critical Questions to Ask
• Process
• Output

Session Resume Detection

Before starting, check for an existing handoff:

1. Check if .planning/HANDOFF.md exists
2. If found: Read it and present to user:
   • Show the phase, task progress, and Next Action from the handoff
   • Ask: "Resume from handoff, or start fresh?"
   • If resume: skip to the recorded phase
   • If fresh: proceed with brainstorm
3. If not found: Proceed normally with Phase 1 (brainstorm)

Context Monitoring

Level	Remaining Context	Action
Normal	>35%	Proceed normally
Warning	25-35%	Complete current question round, then trigger ds-handoff
Critical	≤25%	Immediately trigger ds-handoff — do not start new question rounds

Brainstorming (Questions Only)

Refine vague analysis requests into clear objectives through Socratic questioning. NO data exploration, NO coding - just questions and objectives.

Load shared enforcement first.

Auto-load all constraints matching applies-to: ds:

!uv run python3 ${CLAUDE_SKILL_DIR}/../../scripts/load-constraints.py ds

You MUST have these constraints loaded before proceeding. No claiming you "remember" them.

## The Iron Law of DS Brainstorming

ASK QUESTIONS BEFORE ANYTHING ELSE. This is not negotiable.

Before loading data, before exploring, before proposing approaches, you MUST:

1. Ask clarifying questions using AskUserQuestion
2. Understand what the user actually wants to learn
3. Identify data sources and constraints
4. Define success criteria
5. Only THEN propose analysis approaches

STOP - You're about to load data or explore before asking questions. Don't do this.

What Brainstorm Does

DO	DON'T
Ask clarifying questions	Load or explore data
Understand analysis objectives	Run queries
Identify data sources	Profile data (that's /ds-plan)
Define success criteria	Create visualizations
Ask about constraints	Write analysis code
Check if replicating existing analysis	Propose specific methodology

Brainstorm answers: WHAT and WHY Plan answers: HOW (data profile + tasks) (separate skill)

Critical Questions to Ask

Data Source Questions

• What data sources are available?
• Where is the data located (files, database, API)?
• What time period does the data cover?
• How frequently is the data updated?

Objective Questions

• What question are you trying to answer?
• Who is the audience for this analysis?
• What decisions will be made based on results?
• What would a successful outcome look like?

Constraint Questions

• Are you replicating an existing analysis? (Critical for methodology)
• Are there specific methodologies required?
• What is the timeline for this analysis?
• Are there computational resource constraints?

Output Questions

• What format should results be in (report, dashboard, model)?
• What tables and figures will the final output contain? (The planned-exhibits list — ds-plan maps every exhibit to a canonical "master" dataset so they all share one methodology. Capturing it here, even roughly, is what lets the plan be built around the smallest set of datasets feeding every exhibit.)
• What visualizations are expected?
• How will results be validated?

Process

1. Ask Questions First

Employ AskUserQuestion immediately:

• One question at a time - never batch
• Multiple-choice preferred - easier to answer
• Focus on: objectives, data sources, constraints, replication requirements

Smart-Discuss: Batch Ambiguities

When multiple analysis questions arise, batch them into ONE AskUserQuestion call:

Batched (fast — 1 round-trip):

AskUserQuestion(questions=[
  {"question": "Primary dataset?", "options": [{"label": "CRSP"}, {"label": "Compustat"}, {"label": "Both merged"}]},
  {"question": "Sample period?", "options": [{"label": "2000-2024"}, {"label": "2010-2024"}, {"label": "Custom"}]},
  {"question": "Frequency?", "options": [{"label": "Monthly"}, {"label": "Quarterly"}, {"label": "Annual"}]}
])

When to batch: After understanding the research question, if 3+ independent questions arise, batch them. When NOT to batch: If a question's answer changes what other questions to ask (e.g., dataset choice affects available variables).

2. Identify Replication Requirements

CRITICAL: Ask early if replicating existing work:

AskUserQuestion:
  question: "Are you replicating or extending existing analysis?"
  options:
    - label: "Replicating existing"
      description: "Must match specific methodology/results"
    - label: "Extending existing"
      description: "Building on prior work with modifications"
    - label: "New analysis"
      description: "Fresh analysis, methodology flexible"

When replicating:

• Obtain reference to original (paper, code, report)
• Document exact methodology requirements
• Define acceptable deviation from original results

3. Propose Approaches

After objectives are clear:

• Propose 2-3 different approaches with trade-offs
• Lead with recommendation (mark as "Recommended")
• Use AskUserQuestion for the user to select the preferred approach

4. Write Spec Doc

After selecting an approach:

• Write to .planning/SPEC.md
• Include: objectives, data sources, success criteria, constraints
• NO implementation details - reserve those for /ds-plan

# Spec: [Analysis Name]

> **For Claude:** After writing this spec, discover and load the ds-plan skill for Phase 2:
>Read `${CLAUDE_SKILL_DIR}/../../skills/ds-plan/SKILL.md` and follow its instructions.

## Objective
[What question this analysis answers]

## Data Sources
- [Source 1]: [location, format, time period]
- [Source 2]: [location, format, time period]

## Planned Exhibits
<!-- The tables and figures the final output will contain. Rough is fine — ds-plan Step 5d maps each to a canonical master dataset so all exhibits share one methodology. Omit only for a genuine single-table one-off. -->
- Table 1: [what it shows]
- Table 2: [what it shows]
- Figure 1: [what it shows]

## Requirements

Assign each requirement a unique ID using `CATEGORY-NN` format (e.g., `DATA-01`, `VIZ-02`, `STAT-03`). Categories come from natural groupings in the analysis.

| ID | Requirement | Scope |
|----|-------------|-------|
| [CAT-01] | [Requirement 1] | v1 |
| [CAT-02] | [Requirement 2] | v1 |

Scope: `v1` = must complete, `v2` = nice to have, `out-of-scope` = explicitly excluded.

## Success Criteria
- [ ] [CAT-01] [Criterion]
- [ ] [CAT-02] [Criterion]

## Constraints
- Replication: [yes/no - if yes, reference source]
- Timeline: [deadline]
- Methodology: [required approaches]

## Chosen Approach
[Description of selected approach]

## External Skills Likely In Play
<!-- List plugin skills whose data/tools will be touched. ds-plan Step 5b will Glob their references/ and examples/ before drafting tasks. -->
- [e.g. wrds — holdings/voting data via SAS on WRDS grid]
- [e.g. gemini-batch — LLM extraction for text fields]
- [none]

## Rejected Alternatives
- Option B: [why rejected]
- Option C: [why rejected]

Gate: Exit Brainstorm

Checkpoint type: human-verify (SPEC.md content is machine-verifiable)

Before transitioning to ds-plan, execute this gate:

1. IDENTIFY → SPEC.md exists at `.planning/SPEC.md`
2. RUN      → Read(".planning/SPEC.md")
3. READ     → Verify it contains: Objectives, Data Sources, Requirements (with CATEGORY-NN IDs), Success Criteria sections
4. VERIFY   → User has confirmed the objectives via AskUserQuestion response (not agent self-assessment).
              Check: was AskUserQuestion called and did user respond affirmatively?
5. CLAIM    → Only proceed to ds-plan if ALL checks pass

If ANY check fails, do NOT proceed. Fix the gap first.

Self-assessment is not user confirmation. If the user hasn't explicitly approved the objectives via AskUserQuestion, you haven't finished brainstorm.

Output

Declare brainstorm complete when:

• Analysis objectives clearly understood
• Data sources identified
• Success criteria defined
• Constraints documented (especially replication requirements)
• Approach chosen from alternatives
• .planning/SPEC.md written
• User confirms ready for data exploration

Workflow Context

This skill is Phase 1 of the 5-phase /ds workflow:

┌──────────────┐    ┌──────────┐    ┌──────────────┐    ┌───────────┐    ┌───────────┐
│ ds-brainstorm│───→│ ds-plan  │───→│ ds-implement │───→│ ds-review │───→│ ds-verify │
│  SPEC.md     │    │ PLAN.md  │    │ LEARNINGS.md │    │ APPROVED? │    │ COMPLETE? │
└──────────────┘    └──────────┘    └──────────────┘    └─────┬─────┘    └─────┬─────┘
                                         ↑                    │                │
                                         └── CHANGES REQ'D ───┘                │
                                         ↑                                     │
                                         └──── NEEDS WORK ────────────────────┘

1. Phase 1: ds-brainstorm (current) - Clarify objectives through Socratic questioning
2. Phase 2: ds-plan - Profile data and break analysis into tasks
3. Phase 3: ds-implement - Execute analysis tasks with output-first verification
4. Phase 4: ds-review - Review methodology, data quality, and statistical validity (max 3 cycles)
5. Phase 5: ds-verify - Check reproducibility and obtain user acceptance

No Pause After Brainstorm

**After user confirms objectives, IMMEDIATELY proceed to ds-plan. Do NOT ask "should I continue?" or "ready to proceed?"**

DO NOT:

• Ask "should I continue?" (the user already confirmed objectives — a second confirmation request is a stall, not courtesy)
• Summarize what was agreed (SPEC.md IS the summary; repeating it wastes context)
• Treat this as a stopping point (the workflow is sequential — brainstorm done = plan starts, no gap)

Phase Summary

After writing SPEC.md, update it with structured frontmatter:

---
phase: ds-brainstorm
status: completed
implements: [all requirement IDs assigned in this phase]
requires: [user input]
provides: [.planning/SPEC.md]
affects: [.planning/]
tags: [brainstorm, objectives, requirements]
---

One-liner rule: Must be SUBSTANTIVE. Good: "Panel regression study of CEO pay-performance sensitivity using CRSP-Compustat 2000-2024". Bad: "Brainstorm complete".

Phase Complete

After completing brainstorm, dispatch the spec reviewer before proceeding:

Phase 1: Brainstorm -> SPEC.md written
  -> Dispatch ds-spec-reviewer subagent
  -> If APPROVED -> proceed to ds-plan
  -> If ISSUES_FOUND -> fix SPEC.md -> re-dispatch reviewer (max 5 iterations)

Step 1: Discover and load the spec reviewer skill: Read ${CLAUDE_SKILL_DIR}/../../skills/ds-spec-reviewer/SKILL.md and follow its instructions.

Step 2: Only after reviewer returns APPROVED, discover and load the next phase: Read ${CLAUDE_SKILL_DIR}/../../skills/ds-plan/SKILL.md and follow its instructions.

Fallback (if Read fails): /ds-plan

CRITICAL: Do not skip to analysis implementation. Phase 2 profiles data and breaks down the analysis into discrete, manageable tasks. CRITICAL: Do not skip spec review. An unreviewed spec means profiling the wrong data and planning the wrong analysis.