Market Sizing Skill

Help startup founders build credible, defensible TAM/SAM/SOM analysis — the kind that earns investor trust rather than raising eyebrows. Produce a structured, validated market sizing with external sources, sensitivity testing, and a self-check against common pitfalls. The tone is founder-first: a rigorous but supportive coaching session.

Input Formats

Accept any format: pitch deck (PDF, PPTX, markdown), financial model, market data, text descriptions, or verbal description of the business.

Available Scripts

All scripts are at ${CLAUDE_PLUGIN_ROOT}/skills/market-sizing/scripts/:

• market_sizing.py — TAM/SAM/SOM calculator (top-down, bottom-up, or both)
• sensitivity.py — Stress-test assumptions with low/base/high ranges and confidence-based auto-widening
• checklist.py — Validates 22-item self-check with pass/fail per item
• compose_report.py — Assembles report with cross-artifact validation; --strict exits 1 on high/medium warnings
• visualize.py — Generates self-contained HTML with SVG charts (not JSON)

Run with: python3 ${CLAUDE_PLUGIN_ROOT}/skills/market-sizing/scripts/<script>.py --pretty [args]

Available References

Read as needed from ${CLAUDE_PLUGIN_ROOT}/skills/market-sizing/references/:

• tam-sam-som-methodology.md — Definitions, calculation methods, industry examples, best practices
• pitfalls-checklist.md — Self-review checklist for common mistakes
• artifact-schemas.md — JSON schemas for all analysis artifacts

Artifact Pipeline

Every analysis deposits structured JSON artifacts into a working directory. The final step assembles all artifacts into a report and validates consistency. This is not optional.

Rules:

• Deposit each artifact before proceeding to the next step
• For agent-written artifacts (Steps 1-3), consult references/artifact-schemas.md for the JSON schema
• If a step is not applicable, deposit a stub: {"skipped": true, "reason": "..."}
• Do NOT use isolation: "worktree" for sub-agents — files written in a worktree won't appear in the main $ANALYSIS_DIR

Keep the founder informed with brief, plain-language updates at each step. Never mention file names, scripts, or JSON. After each analytical step (4–6), share a one-sentence finding before moving on.

Workflow

Path Setup

SCRIPTS="$CLAUDE_PLUGIN_ROOT/skills/market-sizing/scripts"
REFS="$CLAUDE_PLUGIN_ROOT/skills/market-sizing/references"
SHARED_REFS="$CLAUDE_PLUGIN_ROOT/references"
if ls "$(pwd)"/mnt/*/ >/dev/null 2>&1; then
  ARTIFACTS_ROOT="$(ls -d "$(pwd)"/mnt/*/ | head -1)artifacts"
elif ls "$(pwd)"/sessions/*/mnt/*/ >/dev/null 2>&1; then
  ARTIFACTS_ROOT="$(ls -d "$(pwd)"/sessions/*/mnt/*/ | head -1)artifacts"
else
  ARTIFACTS_ROOT="$(pwd)/artifacts"
fi

If CLAUDE_PLUGIN_ROOT is empty, fall back: Glob for **/founder-skills/skills/market-sizing/scripts/market_sizing.py, strip to get SCRIPTS, derive REFS.

If ARTIFACTS_ROOT resolves to $(pwd)/artifacts but no artifacts/ directory exists at $(pwd): The workspace may not be mounted yet. Use Glob with pattern **/artifacts/founder_context.json to locate existing artifacts, and derive ARTIFACTS_ROOT from the result. If nothing is found, mkdir -p "$ARTIFACTS_ROOT" and proceed.

ANALYSIS_DIR="$ARTIFACTS_ROOT/market-sizing-{company-slug}"
mkdir -p "$ANALYSIS_DIR"

Steps 1-2: Extract Inputs & Choose Methodology

When files are provided (deck, model, market data), spawn a general-purpose Task sub-agent to read materials and determine methodology. The sub-agent receives: file path(s), SCRIPTS, REFS, SHARED_REFS, and ANALYSIS_DIR paths. Do NOT use isolation: "worktree".

The sub-agent:

1. Reads the provided file(s)
2. Reads $REFS/tam-sam-som-methodology.md
3. Reads $REFS/artifact-schemas.md for inputs.json and methodology.json schemas
4. Extracts all market-relevant data
5. Writes inputs.json to $ANALYSIS_DIR/inputs.json
6. Writes methodology.json to $ANALYSIS_DIR/methodology.json

If the deck includes explicit TAM/SAM/SOM claims, record them in inputs.json under existing_claims. These are used by compose_report.py and visualize.py to compare deck claims against calculated figures.

Instruct the sub-agent to return ONLY:

1. File paths written
2. Company brief: name, product description, geography, target segments, pricing model, revenue model type
3. Quantitative data found: revenue, customer count, ARPU, growth rates, headcount (actual values, not the full inputs.json)
4. Existing claims: actual TAM/SAM/SOM numbers from the deck (if found), with slide/section reference
5. Methodology: chosen approach + rationale
6. Data availability: which key fields are populated vs missing
7. List of missing/unclear fields that the founder should clarify

Do not echo the full artifacts or raw document content. The company brief must be rich enough for the main agent to direct web research, construct sizing calculations, perform reality checks, and provide contextual coaching — without needing to re-read the source materials.

After the sub-agent returns, review the summary. If missing fields are flagged, ask the founder and patch inputs.json. Share a brief update.

When conversational input (no files): Handle directly in the main agent — the data is already in the conversation. Read references/tam-sam-som-methodology.md, choose the approach, and write both artifacts directly.

Graceful degradation: If Task tool is unavailable, extract directly in the main agent.

Step 3: External Validation -> validation.json

When methodology is "both", spawn 2 general-purpose Task sub-agents in a single message (parallel, no isolation: "worktree"). Each receives: company description, product/service, geography, segments from inputs.json, and methodology context.

• Sub-agent A (Top-down research): WebSearch for industry reports, government statistics, analyst estimates for total market size, segment percentages, market growth rates.
• Sub-agent B (Bottom-up research): WebSearch for customer counts, pricing/ARPU benchmarks, competitor data, serviceable segment data. Also receives: pricing model, customer profile.

Each returns ONLY: (1) structured assumptions array [{name, value, source_url, source_title, quality_tier, confidence, category}], (2) key market figures found, (3) source count and quality distribution. Do not echo raw search results.

Main agent consolidates both sets of findings into validation.json, cross-validates between approaches, and flags discrepancies.

When methodology is single (top-down or bottom-up), spawn 1 sub-agent for the chosen approach. Same return contract. Main agent writes validation.json.

When pure calculation (user provides all numbers, no validation needed): Handle directly — no sub-agent.

Source quality hierarchy: Government/regulatory > Established analysts > Industry associations > Academic > Business press > Company blogs (product facts only).

Triangulate key numbers with 2+ independent sources. Track every source with quality tier and segment match. Every assumption must appear in the assumptions array with a name matching script parameter names and a category of sourced, derived, or agent_estimate.

Graceful degradation: If Task tool is unavailable, research directly in the main agent.

Step 4: Calculate TAM/SAM/SOM -> sizing.json

cat <<'SIZING_EOF' | python3 "$SCRIPTS/market_sizing.py" --stdin --pretty -o "$ANALYSIS_DIR/sizing.json"
{...sizing input JSON — see artifact-schemas.md for format...}
SIZING_EOF

For "both" mode, check the comparison section — a >30% TAM discrepancy means investigating which assumptions are flawed. TAM must match the product's actual target universe (not inflated industry totals).

Multi-vertical / platform companies: If inputs.json lists applications in 2+ distinct industries:

1. Identify verticals — classify as commercial (revenue/pilots), r_and_d (demonstrated feasibility, 2-3yr commercialization path), or future (conceptual/early).
2. Include commercial and r_and_d in TAM. If top-down only covers one vertical, use bottom-up as primary. When verticals have different ARPUs, compute weighted blended ARPU. Future verticals go in coaching commentary as upside, not in the calculated TAM.
3. Narrow SAM and SOM — SAM = traction + active R&D segments. SOM = beachhead only.
4. Document scope in methodology.json rationale.

Default to full-scope TAM. Only narrow to beachhead if the user explicitly requests it.

Step 4.5: Reality Check

Before proceeding, answer:

1. Laugh test: Would an experienced VC nod or raise an eyebrow? Seed + <5 pilots + >$1B TAM = explain yourself.
2. Scope match: Does TAM cover all commercial and r_and_d verticals from inputs.json?
3. Customer count sanity: Can you name a representative sample of the customers in your count?
4. Convergence integrity: Were top-down and bottom-up parameters set independently? If you adjusted one after seeing the other, revert and accept the delta.

This step produces no artifact. If it reveals problems, fix them before proceeding.

Steps 5 & 6: Parallel Analysis (Sensitivity + Checklist)

Spawn 2 general-purpose Task sub-agents in a single message (parallel, no isolation: "worktree") after Step 4.5 reality check passes. Each receives the expanded SCRIPTS, REFS, and ANALYSIS_DIR paths.

Sub-agent A — Sensitivity:

Reads $ANALYSIS_DIR/validation.json for confidence tiers and $ANALYSIS_DIR/sizing.json for base values and approach. Constructs sensitivity input with confidence-based ranges and runs sensitivity.py.

Tag each parameter with confidence from validation: sourced (range stands), derived (min +/-30%), agent_estimate (min +/-50%). Include every agent_estimate parameter — compose_report.py flags missing ones as UNSOURCED_ASSUMPTIONS.

cat <<'SENS_EOF' | python3 "$SCRIPTS/sensitivity.py" --pretty -o "$ANALYSIS_DIR/sensitivity.json"
{...sensitivity input JSON — see artifact-schemas.md for format...}
SENS_EOF

Instruct Sub-agent A to return ONLY: (1) file path written, (2) most_sensitive parameter, (3) top 3 sensitivity ranking entries (parameter + SOM swing %).

Sub-agent B — Checklist:

Reads $REFS/pitfalls-checklist.md for the 22 criteria and all prior artifacts (inputs.json, methodology.json, validation.json, sizing.json). Assesses all 22 items with status and notes. Read $REFS/artifact-schemas.md "Canonical 22 checklist IDs" section first.

cat <<'CHECK_EOF' | python3 "$SCRIPTS/checklist.py" --pretty -o "$ANALYSIS_DIR/checklist.json"
{"items": [
  {"id": "structural_tam_gt_sam_gt_som", "status": "pass", "notes": null},
  ...all 22 items...
]}
CHECK_EOF

Instruct Sub-agent B to return ONLY: (1) file path written, (2) score_pct, (3) overall_status, (4) list of failed items.

Graceful degradation: If Task tool is unavailable, run Steps 5-6 sequentially in the main agent.

After both sub-agents return, share a coaching update with the founder before proceeding to Step 7.

Step 7: Compose and Validate Report

python3 "$SCRIPTS/compose_report.py" --dir "$ANALYSIS_DIR" --pretty -o "$ANALYSIS_DIR/report.json"

Fix high-severity warnings and re-run. Use --strict to enforce a clean report.

Primary deliverable: Read report_markdown from the output JSON, write it to $ANALYSIS_DIR/report.md, and display it to the user in full. Present the file path so the user can access it directly. Then add coaching commentary: what to feel confident about, the highest-leverage fix, whether the market story holds together, and which 1-2 sensitivity parameters to prioritize sourcing.

Step 8 (Optional): Generate Visual Report

python3 "$SCRIPTS/visualize.py" --dir "$ANALYSIS_DIR" -o "$ANALYSIS_DIR/report.html"

Present the HTML file path to the user so they can open the visual report.

Step 9: Deliver Artifacts

Copy final deliverables to workspace root: {Company}_Market_Sizing.md, .html (if generated), .json (optional).

Scoring

• Each of 22 items: pass / fail / not_applicable
• score_pct = pass / (total - not_applicable) x 100
• compose_report.py validates cross-artifact consistency (assumption coverage, sensitivity ranges)