Fp Brief

What it does

When your agent uses it

• : understanding why decisions were made
• Onboarding to feature reasoning
• Reviewing decision chains
• Explaining doc from first principles

Example prompts

• “/fp-brief”

Requirements

• Pre-approved tools (allowed-tools): Read, Grep, Glob, Write, Bash(node:*)

Workflow steps

3 steps, taken from the step headings in SKILL.md.

1. 1Input Resolution
2. 2First-Principles Extraction
3. 3Output Assembly

What it can do on your machine

Read from SKILL.md and the folder at commit a4d4bc1. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Read
  • Grep
  • Glob
  • Write
  • Bash(node:*)

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are mermaid and markdown).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Fp Brief loads about 1.8k tokens when it runs, and up to ~5.5k if it reads all its reference files. Until then it costs about 99 tokens; SKILL.md has 534 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~99

When it runs · the whole SKILL.md, loaded when a task matches

~1.8k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~5.5k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from sd0xdev/sd0x-harness at commit a4d4bc1, republished under its MIT licence (© sd0xdev). 534 words, ~1,822 tokens.

name

fp-brief

description

First-principles briefing from technical documents. Use when: understanding why decisions were made, onboarding to feature reasoning, reviewing decision chains, explaining doc from first principles. Not for: PM/CTO summary (use project-brief), pre-doc analysis (use feasibility-study), code explanation (use codex-explain). Output: structured reasoning chain with sensitivity analysis.

allowed-tools

Read, Grep, Glob, Write, Bash(node:*)

/fp-brief <doc-path> [--depth brief|normal|deep] [--verify off|codex] [--output <path>] [--no-save]

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

# First-Principles Briefing: <title>

> Source: <path> | Depth: <level> | Format: <type> | Generated: <timestamp>

## 1. Root Problem
## 2. Assumptions Register
## 3. Reasoning Chain
## 4. Alternative Rejection Log
## 5. Decision Sensitivity
## 6. Open Unknowns
## 7. Verification Delta (optional)

Input: /fp-brief docs/features/seek-verdict/2-tech-spec.md
Action: Read spec → detect tech-spec → extract 6 sections → write 2-tech-spec-fp-brief.md

Input: /fp-brief docs/features/auth/2-tech-spec.md --depth brief
Action: Read spec → extract Root Problem + top assumptions + key decisions + top sensitivity → brief output

Input: /fp-brief docs/features/auth/2-tech-spec.md --depth deep --verify codex
Action: Read spec → full extraction → Codex independent verification → write with Verification Delta

Input: /fp-brief notes/design-decisions.md --no-save
Action: Read doc → detect unknown format → generic extraction → print to stdout

© sd0xdev, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 4 other files (references) in skills/fp-brief of sd0xdev/sd0x-harness.

• SKILL.md
• references/codex-verify-prompt.md
• references/detection-rules.md
• references/extraction-guide.md
• references/output-template.md

Open the folder on GitHubat commit a4d4bc1