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Math via Code — Skill Setup

Source: tommulkins/hermes-skill-math-via-code Stars: 0 ⭐ | License: MIT Created: June 24, 2026 Category: Development / Accuracy / Financial Analysis

1. What It Is

A Hermes Agent skill that enforces a hard rule: all arithmetic with 3+ numbers goes through code execution. No exceptions. Born from repeated errors in financial modeling — SDE calculations, P&L analysis, and facility rollups where a single transposed digit cascaded into incorrect deal evaluations.

Core philosophy: LLM arithmetic accuracy degrades sharply past ~150k context tokens and is unreliable even below that. Code is always right; in-head math is not.

What It Handles

  • Financial analysis: SDE, P&L, margins, royalties, annualizations
  • Growth rates, ratios, percentages, weighted averages
  • Unit conversions, projections, multi-facility rollups
  • Reading data from files/APIs and computing derived values
  • Excel-specific pitfalls (whitespace stripping, data_only=True, etc.)

When NOT to Use

  • Single-operation arithmetic on two numbers (5 * 3, 100 - 20) — these are safe in-head
  • Pure text manipulation or formatting tasks

2. Prerequisites

  • Hermes Agent
  • No additional packages required (uses built-in execute_code)

3. Installation

hermes skills install https://raw.githubusercontent.com/tommulkins/hermes-skill-math-via-code/main/SKILL.md --category software-development --name math-via-code -y

Verify

hermes skills list | grep math-via-code

4. How It Works

Decision Flow

Numbers provided? → Count them:
  ├── 0-2 numbers → Safe for in-head math (e.g., 5 * 3)
  └── 3+ numbers → ROUTE TO CODE (execute_code or Python script)

Procedure

  1. Determine inputs — Capture numbers as variables from conversation, files, or APIs. Never re-type from memory.
  2. Write the calculation — Use execute_code for in-memory math; use terminal with project venv for packages (openpyxl, pandas).
  3. Self-check — Include assertions or cross-checks against source data.

Example: SDE Calculation

# Instead of in-head math, the skill routes to:
revenue = 327158
direct_costs = 192193
gp = revenue - direct_costs

overhead_items = [960, 1351.92, 9000, 1440, 1137.24]
overhead_royalties = round(revenue * 0.07, 2)
total_overhead = sum(overhead_items) + overhead_royalties

sde = gp - total_overhead
print(f"SDE: ${sde:,.2f}")

5. Data Sources

Source Guidance
Conversation Capture numbers as Python variables directly
Excel/CSV Use openpyxl with data_only=True; strip whitespace from all cell values
API responses Parse JSON, validate numeric fields, handle null/missing values
Multi-file Cross-reference with assertions (e.g., assert sum(details) == total, "Mismatch")

6. CorpusIQ Use Cases

Use Case Application
Lead qualification math LTV calculations, churn projections, CAC payback periods
Pricing analysis Margin calculations, tier comparisons, bundling economics
Growth metrics MoM/ YoY growth rates, cohort retention math
Agent cost tracking Token cost aggregation, per-agent cost allocation, budget burn rates
Financial reporting Revenue rollups across multiple data sources

7. Troubleshooting

Symptom Cause Fix
Skill doesn't trigger Calculation is simple (2 numbers) Only 3+ number operations trigger the skill
Excel values wrong data_only=False returns formulas Use openpyxl.load_workbook(file, data_only=True)
Whitespace breaks numbers Cells have trailing spaces .strip() all cell values before conversion
Assertion fails Source data inconsistent Report the mismatch — don't silently proceed

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