doubt-driven-development

doubt-driven-development is a skill for Claude Code, Codex from mycelium-hq/ai-brain-starter. It costs 104 tokens per session (3,577 once invoked), scanned A, a copy of doubt-driven-development, MIT.

A review practice for checking uncertain coding decisions and non-trivial changes with a deliberate attempt to disprove assumptions.

In plain words
What is it for?
Use it before committing complex code, choosing an architecture, crossing service boundaries, or making changes involving deployment, data, or public APIs.
Why use it?
It helps catch mistakes that the compiler cannot detect, especially when working in unfamiliar code or changing production behavior.

Skill for Claude CodeCodex

Written for Claude Code and Codex: shipped in a Claude Code plugin, but also runs codex exec. Also seen: mentions subagents; mentions Claude Code; mentions Codex.

Part of the ai-brain-starter plugin — 38 skills, 17 commands, 3 agents, 1 hook shipped together

Good fit Use it before committing complex code, choosing an architecture, crossing service boundaries, or making changes involving deployment, data, or public APIs.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/mycelium-hq/ai-brain-starter/doubt-driven-development
Install

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.

Any agent
npx skills add mycelium-hq/ai-brain-starter --skill doubt-driven-development
Clone the repo
git clone --depth 1 https://github.com/mycelium-hq/ai-brain-starter

Made for: Claude Code, Codex.

Or install ai-brain-starter, the plugin that ships this one along with the rest of its 38 skills, 17 commands, 3 agents, 1 hook.

Wrote 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.

agentmods badge for doubt-driven-development

README.md
[![agentmods](https://agentmods.dev/badge/skills/mycelium-hq/ai-brain-starter/doubt-driven-development.svg)](https://agentmods.dev/skills/mycelium-hq/ai-brain-starter/doubt-driven-development)
Your own site
<a href="https://agentmods.dev/skills/mycelium-hq/ai-brain-starter/doubt-driven-development"><img src="https://agentmods.dev/badge/skills/mycelium-hq/ai-brain-starter/doubt-driven-development.svg" alt="Measured on agentmods" height="20"></a>
Per session 104 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,577 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 89% copy Near-identical to another mod in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00104 $0.03577
Opus 5 $0.00052 $0.01788
Sonnet 5 $0.00021 $0.00715
Haiku 4.5 $0.00010 $0.00358

Measured 8d ago against content hash 16eecbed1ff1, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

doubt-driven-development 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 8d 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.

Origin

This is a copy

89% identical to doubt-driven-development — 36 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/doubt-driven-development/SKILL.md · 246 lines

How it starts

The opening of the file, as written. The whole thing — 246 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Doubt-Driven Development

Cherry-picked from addyosmani/agent-skills (MIT) 2026-05-26. Adapted to this substrate.

Overview

A confident answer is not a correct one. Long sessions accumulate context that quietly turns assumptions into "facts" without anyone noticing. Doubt-driven development is the discipline of materializing a fresh-context reviewer — biased to disprove, not approve — before any non-trivial output stands.

This is not a post-PR review. Post-PR review is a verdict on a finished artifact. This is an in-flight posture: non-trivial decisions get cross-examined while course-correction is still cheap.

When to Use

A decision is non-trivial when at least one of these is true:

  • It introduces or modifies branching logic
  • It crosses a module or service boundary
  • It asserts a property the type system or compiler cannot verify (thread safety, idempotence, ordering, invariants)
  • Its correctness depends on context the future reader cannot see
  • Its blast radius is irreversible (production deploy, data migration, public API change)

Apply the skill when:

  • About to make an architectural decision under uncertainty
  • About to commit non-trivial code
  • About to claim a non-obvious fact ("this is safe", "this scales", "this matches the spec")
  • Working in code you don't fully understand

When NOT to use:

  • Mechanical operations (renaming, formatting, file moves)
  • Following a clear, unambiguous user instruction
  • Reading or summarizing existing code
  • One-line changes with obvious correctness
  • Pure tooling operations (running tests, listing files)
  • The user has explicitly asked for speed over verification

If you doubt every keystroke, you ship nothing. The skill applies only to non-trivial decisions as defined above.

Loading Constraints

This skill is designed for the main-session orchestrator, where Step 3 (DOUBT) can spawn a fresh-context reviewer.

  • Do NOT add this skill to a subagent's skills: frontmatter. A subagent that follows Step 3 would spawn another subagent, which Claude Code blocks by construction (subagents cannot spawn subagents).
  • If you find yourself applying this skill inside a subagent context: surface to the user that doubt-driven cannot run nested, and let the main session handle it. As a last resort only, a degraded self-questioning fallback exists — rewrite ARTIFACT + CONTRACT as a fresh self-prompt with a hard mental separator from your prior reasoning, and walk Steps 1–5. Flag the result as degraded and prefer escalation whenever the user is reachable.

Read the full file on GitHub · 246 lines

Changes

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.

  1. 8d ago First seen · 246 lines · 104 tokens per session scan A 16eecbed1ff1

Subscribe to this mod's changes

doubt-driven-development is a skill published in the GitHub repository mycelium-hq/ai-brain-starter (36 stars, last pushed yesterday), licensed MIT. It adds 104 tokens to every session and 3,577 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. It is 89% identical to doubt-driven-development, differing in 36 lines, and is treated as a copy.

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