Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add axiomantic/spellbook --skill design-explorationgit clone --depth 1 https://github.com/axiomantic/spellbookWrote 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/axiomantic/spellbook/design-exploration)<a href="https://agentmods.dev/skills/axiomantic/spellbook/design-exploration"><img src="https://agentmods.dev/badge/skills/axiomantic/spellbook/design-exploration/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/axiomantic/spellbook/design-exploration"><img src="https://agentmods.dev/badge/skills/axiomantic/spellbook/design-exploration.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Rogue Agent · line 99 Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
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 | $0.00088 | $0.01693 |
| Opus 5.5 | $0.00035 | $0.00677 |
| Sonnet 5.5 | $0.00018 | $0.00339 |
| Haiku 4.5 | $0.00009 | $0.00169 |
Grade A, and why
design-exploration 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 181 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Design Exploration
Invariant Principles
- One Question Per Turn - Single questions get better answers. Wrong: "What's the goal and what are your constraints?" Right: "What problem does this solve?"
- Explore Before Committing - Propose 2-3 approaches with trade-offs before settling.
- Incremental Validation - Present designs in digestible sections; confirm understanding.
- YAGNI Ruthlessly - Simplest design that solves the problem.
- Context Determines Mode - Synthesis when context complete; interactive when discovery needed.
Inputs
| Input | Required | Description |
|---|---|---|
context.feature_idea |
Yes | User's description of what they want to create/modify |
context.constraints |
No | Known constraints (tech stack, performance, timeline) |
context.existing_patterns |
No | Patterns from codebase research |
context.mode_override |
No | "SYNTHESIS MODE" to skip discovery |
Outputs
| Output | Type | Description |
|---|---|---|
design_document |
File | Design doc at ~/.local/spellbook/docs/<project>/plans/YYYY-MM-DD-<topic>-design.md |
approach_decision |
Inline | Selected approach with rationale for alternatives considered |
implementation_ready |
Boolean | Whether design is complete enough to proceed |
Mode Detection
Synthesis mode active when context contains:
- "SYNTHESIS MODE" / "Mode: AUTONOMOUS" / "DO NOT ask questions"
- "Pre-Collected Discovery Context" or "design_context"
- Comprehensive architectural decisions, scope boundaries, success criteria already defined
| Mode | Behavior |
|---|---|
| Synthesis | Skip discovery. Make autonomous decisions. Document rationale. Write complete design. |
| Interactive | Ask questions one at a time. Validate incrementally. Collaborate. |
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.
- 1mo ago First seen · 181 lines · 88 tokens per session scan A bc6784cff26b
design-exploration is a skill published in the GitHub repository axiomantic/spellbook (10 stars, last pushed 2d ago), licensed MIT. It adds 88 tokens to every session and 1,693 once invoked, about $0.0004 per session on Opus 5.5. 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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confirm-failures-are-causally-linked-to-the-task-before-reportin
When delegating a task affected by this skill, include.