Borrowing it
Nothing to install: this file belongs to tellahq/opensession. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/tellahq/opensession/main/.agents/skills/pstack-suite/skills/principle-subtract-before-you-add/SKILL.mdgit clone --depth 1 https://github.com/tellahq/opensessionWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/tellahq/opensession/principle-subtract-before-you-add)<a href="https://agentmods.dev/skills/tellahq/opensession/principle-subtract-before-you-add"><img src="https://agentmods.dev/badge/skills/tellahq/opensession/principle-subtract-before-you-add/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/tellahq/opensession/principle-subtract-before-you-add"><img src="https://agentmods.dev/badge/skills/tellahq/opensession/principle-subtract-before-you-add.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00039 | $0.00261 |
| Opus 5 | $0.00019 | $0.00130 |
| Sonnet 5 | $0.00008 | $0.00052 |
| Haiku 4.5 | $0.00004 | $0.00026 |
Grade A, and why
principle-subtract-before-you-add scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
Copies of this mod
6 near-identical copies found in the catalogue:
- principle-subtract-before-you-add — 100% identical, 0 lines differ
- principle-subtract-before-you-add — 100% identical, 0 lines differ
- principle-subtract-before-you-add — 97% identical, 4 lines differ
- principle-subtract-before-you-add — 97% identical, 9 lines differ
- principle-subtract-before-you-add — 97% identical, 9 lines differ
- principle-subtract-before-you-add — 97% identical, 1 lines differ
What it actually says
Subtract Before You Add
When evolving a system, remove complexity first, then build. Deletion gives you a simpler base, which makes the next addition smaller and less brittle.
Why: Adding to a complex system compounds complexity. Removing first cuts the surface area, reveals the essential structure, and usually makes the next design obvious. Default to subtraction.
Make simplification a continual investment. Leave the design slightly simpler and more capable behind the same or smaller surface than you found it.
The pattern:
- Sequence removal before construction
- Cut before you polish (get to the minimum before investing in quality)
- Design for observed usage, not speculative edge cases
- No speculative validators, parsers, or guards beyond what the spec demands
- Out-of-spec features drag validators behind them. Persistence, retry-on-startup, and schema migration each need guards to defend their inputs.
- Simplify prompts (remove redundant instructions, excessive templates)
- When a reference has no novel content, delete it rather than leaving a stub
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 6d ago First seen · 23 lines · 39 tokens per session scan A 3999888dc21c
principle-subtract-before-you-add is a skill published in the GitHub repository tellahq/opensession (366 stars, last pushed yesterday), licensed MIT. It adds 39 tokens to every session and 261 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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