fp-brief

fp-brief is a skill for Claude Code, Codex from sd0xdev/sd0x-harness. It costs 77 tokens per session (1,791 once invoked), scanned A, original, MIT.

A briefing skill that explains the reasoning behind decisions in technical documents. It examines assumptions, decision chains, and which choices matter most.

In plain words
What is it for?
Creating an onboarding brief from a technical document, checking assumptions, and explaining why decisions were taken.
Why use it?
It helps readers understand not only what a document says, but why its decisions were made.

Skill for Claude CodeCodex

Part of the sd0x-dev-flow plugin — 98 skills, 16 agents, 5 hooks shipped together

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.

agentmods
npx agentmods add skills/sd0xdev/sd0x-harness/fp-brief
Any agent
npx skills add sd0xdev/sd0x-harness --skill fp-brief
Clone the repo
git clone --depth 1 https://github.com/sd0xdev/sd0x-harness

Made for: Claude Code, Codex.

Or install sd0x-dev-flow, the plugin that ships this one along with the rest of its 98 skills, 16 agents, 5 hooks.

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 fp-brief

README.md
[![agentmods](https://agentmods.dev/badge/skills/sd0xdev/sd0x-harness/fp-brief.svg)](https://agentmods.dev/skills/sd0xdev/sd0x-harness/fp-brief)
Your own site
<a href="https://agentmods.dev/skills/sd0xdev/sd0x-harness/fp-brief"><img src="https://agentmods.dev/badge/skills/sd0xdev/sd0x-harness/fp-brief.svg" alt="Measured on agentmods" height="20"></a>
Per session 77 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,791 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found 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 $0.00077 $0.01791
Opus 5 $0.00039 $0.00896
Sonnet 5 $0.00015 $0.00358
Haiku 4.5 $0.00008 $0.00179

Measured today against content hash c94ccc580fb9, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

fp-brief 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 today.

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.

skills/fp-brief/SKILL.md · 175 lines

How it starts

The opening of the file, as written. The whole thing — 175 lines — stays where its author put it; the contents beside it link to each section on GitHub.

First-Principles Briefing Skill

Trigger

  • Keywords: first principles, fp brief, why was this decided, reasoning chain, decision sensitivity, explain decisions, assumption analysis, onboarding brief

When NOT to Use

Scenario Alternative
PM/CTO executive summary (strip technical details) /project-brief
Pre-doc feasibility analysis (before writing spec) /feasibility-study
Code explanation at function/file level /codex-explain
Code architecture overview /code-explore
Simple document summary Ask Claude directly

Command Signature

/fp-brief <doc-path> [--depth brief|normal|deep] [--verify off|codex] [--output <path>] [--no-save]
Flag Default Description
<doc-path> Required Source markdown document path
--depth normal Output detail level
--verify off Independent Codex reasoning verification
--output Same dir, -fp-brief.md suffix Custom output path
--no-save false Print to stdout instead of file

Workflow

sequenceDiagram
    participant U as User
    participant S as /fp-brief
    participant D as Source Doc
    participant O as Output File
    participant X as Codex (optional)

    U->>S: /fp-brief <doc-path> [--depth] [--verify]
    Note over S: Phase 1: Input Resolution
    S->>S: Validate path (repo boundary)
    S->>D: Read source document
    S->>S: Redaction scan (fail-safe)
    S->>S: Auto-detect format (hybrid)
    Note over S: Phase 2: First-Principles Extraction
    S->>S: Extract Root Problem (5-Why)
    S->>S: Build Assumptions Register
    S->>S: Build Reasoning Chain
    S->>S: Build Alternative Rejection Log
    S->>S: Build Decision Sensitivity
    S->>S: Identify Open Unknowns
    Note over S: Phase 3: Output Assembly
    S->>O: Write *-fp-brief.md
    alt --verify codex
        S->>X: Independent reasoning verification
        X-->>S: Verification Delta
        S->>O: Append Verification Delta
    end
    S-->>U: Report complete

Read the full file on GitHub · 175 lines

Files

What ships with it

4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. today Changed c94ccc580fb9
  2. 6d ago First seen · 175 lines · 77 tokens per session scan A e6934faa55c2

Subscribe to this mod's changes

fp-brief is a skill published in the GitHub repository sd0xdev/sd0x-harness (188 stars, last pushed today), licensed MIT. It adds 77 tokens to every session and 1,791 once invoked, about $0.0004 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 2026-08-30.

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