fdf

README

FDF — Feature Document Format

Documentation-as-a-directory for software features. Each feature is a Markdown + Gherkin document; its design spec, plan, acceptance tests, and optional surface/log trail live as stem-qualified siblings beside it; tasks live only under a paired slug/ directory; post-delivery change requests and bug fixes live under changes/; the recurring mechanisms every feature must follow the same way live as practices, and what the project has said but not yet done everywhere is written down as debt; an opinionated CLI validates the whole bundle so it can never silently drift.

docs/features/
├── INDEX.md                      # bundle root (pins fdf_version)
├── LOG.md
├── SPEC.md                       # the format spec, shipped in the bundle
├── STACK.md                      # Context: technology stack
├── ARCHITECTURE.md               # Context: architecture & principles
├── SURFACES.md                   # Context: interface principles (all surfaces)
├── INFRA.md                      # Context: build & deployment infra
├── DOMAIN.md                     # Context: the project's domain language
├── changes/                      # post-delivery work (flat or grouped)
│   ├── INDEX.md
│   └── refund-rounding.md        # type: Fix — the code drifted from the doc
├── debts/                        # known gaps between doc and code
│   ├── INDEX.md
│   └── authz-legacy-handlers.md  # type: Debt — open | accepted | resolved
├── practices/                    # how recurring mechanisms are done
│   ├── INDEX.md
│   └── permission-checks.md      # type: Practice — binding on all code
└── payments/
    ├── INDEX.md
    ├── instant-refunds.md        # Feature: Gherkin scenarios + status
    ├── instant-refunds.spec.md   # approved design (type: Spec)
    ├── instant-refunds.plan.md   # links every task (type: Plan)
    ├── instant-refunds.test.md   # scenario -> concrete proof (type: Test)
    ├── instant-refunds.surface.md  # optional (type: Surface)
    ├── instant-refunds.log.md    # optional feature decisions
    └── instant-refunds/          # task directory ONLY
        ├── 01-refund-api.md
        └── 02-refund-ui.md

Documents are living or episodic, and that decides what happens when the software changes. Living documents describe the system today — the feature's Gherkin, slug.test.md, slug.surface.md, practices, debts, the Context docs — and are amended in place. Episodic documents are frozen records of one piece of work — slug.spec.md, slug.plan.md, tasks, changes, log entries — and are never rewritten. So a delivered feature that changes keeps one feature document, whose Gherkin is edited, and gains a new episode under changes/. Its original spec and plan stay untouched: they record how it was first built, which is the context you need to judge the change.

A Change alters what a delivered feature does; a Fix restores behavior the feature document already describes. Both name the features they touch in affects: — so one bug spanning several features, or one request spanning them, is a single document. Both declare the effects they will have, and rule F10 refuses to let one reach done while the features it claims to alter still describe the old behavior. That is the drift FDF exists to prevent, enforced rather than hoped for.

The five Context documents (STACK.md, ARCHITECTURE.md, SURFACES.md, INFRA.md, DOMAIN.md) are the project's living stack / architecture / surface-principles / infrastructure / vocabulary snapshot. SURFACES.md is always defined at the bundle root (interface principles for APIs, UIs, CLIs, events, and inputs — not “UI only”); feature-level slug.surface.md is optional when a feature needs extra surface detail. fdf init scaffolds all five as stubs; the fdf-init skill interview fills them. They are critical and change only with explicit human approval — accurate context is what makes this agentic engineering, not vibe coding.

DOMAIN.md is the project's domain language: one canonical name per concept and the words banned in its place. The same thing called Item in one document, Product in another and SKU in a third is three things to every reader, and that drift reaches schemas and endpoints. It is the project's internal vocabulary — the bundle and the code's identifiers — not the words a surface shows to people: a UI label or locale string may say "store" for a Venue on purpose, and the skills treat that as a surface decision, never as drift. Rule F12 reports a banned word found in a feature's Gherkin — a warning by default, an error under fdf validate --strict-domain.

Practices (practices/<slug>.md, type: Practice) are the project's binding answers to how do we do X for one recurring mechanism — authorization, permission checks, payment capture, database access. They exist so the answer is written once and followed, instead of being re-derived differently in every feature spec, and so ARCHITECTURE.md does not have to swallow every mechanism to keep them written down. A practice is living and has no episodic trail; its applies-to paths are how later work finds it, since a feature never lists the practices it follows. Rule F11 keeps them honest: a non-empty # Rules, no Gherkin, and a superseded practice that names its replacement.

Debt (debts/<slug>.md, type: Debt) is the register of known gaps between what the project says and what the code does: work deliberately left undone, and rules the codebase does not follow everywhere yet. That second case is what lets a practice be written honestly for an existing codebase — the practice states the rule, the debt names the files that have not caught up, and neither document has to lie for the other to exist. A debt is a register entry, not a unit of work: the work that closes it is a Change, a Fix, or plain code work. Rule F13 means it cannot be closed without saying what closed it (# Resolution), cannot be kept without saying why (# Rationale on accepted), and — through R1 on its resource paths — cannot go on naming code that no longer exists.

Why

Agents made writing code cheap. What broke is the record of why the code exists: the design lived in a chat scrollback that is gone, the plan was never written down, and the tests prove whatever the code happens to do. That is vibe coding, and it compounds — every future change starts from archaeology.

FDF is the opposite bet: the documentation is the interface between humans and agents. Intent, design, plan, and proof live in the repo beside the code; a feature's status must say what is actually true of it; and fdf validate turns drift into a failing build instead of a discovery six months later. Humans approve specs and context; agents do the mechanical work in between. Built for agentic engineering, not vibe coding.

Install

• One-liner (macOS/Linux, no Go needed):

curl -fsSL https://raw.githubusercontent.com/GiteshDalal/fdf/main/install.sh | bash

• Binaries on the releases page
• With mise

mise use ubi:GiteshDalal/fdf

• With Go

go install github.com/GiteshDalal/fdf/cli/cmd/fdf@latest

Use

fdf init                     # scaffold docs/features/ + SPEC.md + context stubs (or FDF_ROOT_DIR / --root)
                             #   then run the fdf-init skill to fill STACK/ARCHITECTURE/SURFACES/INFRA/DOMAIN
fdf new payments/instant-refunds
fdf validate                 # F1-F12 + R1; exit 1 on any violation
fdf validate --strict-domain # …and F12 banned words become errors, not warnings
fdf practice permission-checks  # scaffold a Practice under practices/

fdf debt                     # the register: status, id, filing date, title
fdf debt --open              # …only what is outstanding (also --accepted, --resolved)
fdf debt authz-legacy-handlers  # file a new debt
fdf debt --cleanup           # fold resolved debts into debts/LOG.md and clear them
fdf debt --cleanup --dry-run # …show the plan first, change nothing
fdf spec                     # print the format spec (-v 0.4 for an older one)
fdf help                     # every command with examples
fdf serve                    # browse the bundle (bun x mdts)

# after a feature ships
fdf change --affects payments/instant-refunds refund-window   # behavior should differ
fdf fix    --affects payments/instant-refunds refund-rounding # code drifted from the doc
fdf history payments/instant-refunds                          # what happened since it shipped
fdf release 1.2.0            # derive the release doc from `version:` fields; --ship to close it
fdf install claude-code      # user-level skills + "## Feature Document Format" primer
fdf install codex            #   (primer skipped if the heading is already present)
fdf install opencode
fdf install --project claude-code   # project-level: skills under .claude/, primer in ./CLAUDE.md
fdf migrate                  # mechanical upgrade to the current spec version

fdf install defaults to user-level (under your home directory). Prefer fdf install --project <harness> for repos that actually carry an FDF bundle: skills and the primer stay out of unrelated projects, and a stale primer after fdf migrate is a per-repo refresh instead of a machine-global one. User-level and project-level installs coexist and upgrade independently (each destination has its own .fdf-version markers). A machine with both will carry two primers — harnesses merge memory files, so that is fine.

Scope	Harness	Skills	Instruction file
user	claude-code	~/.claude/skills/	~/.claude/CLAUDE.md
user	codex	~/.codex/skills/	~/.codex/AGENTS.md
user	opencode	~/.config/opencode/skills/	~/.config/opencode/AGENTS.md
project	claude-code	<proj>/.claude/skills/	<proj>/CLAUDE.md
project	codex	<proj>/.codex/skills/	<proj>/AGENTS.md
project	opencode	<proj>/.opencode/skills/	<proj>/AGENTS.md

The agent-facing surface is skills only — eight of them, identical across harnesses. Earlier versions also shipped Claude Code slash commands; those wrapped skills the model can reach directly, so fdf install now removes them (leaving any commands you wrote yourself alone).

--project outside a git working tree is a usage error (exit 2). fdf install --root <dir> (or FDF_ROOT_DIR) bakes a non-default bundle location into the installed skills, which otherwise reference docs/features/; it composes with --project unchanged. Agents need no prior FDF knowledge: the spec copy at the bundle root is the reference the skills and primer point them to.

Works the same everywhere: the bundle may be a plain directory or a git submodule mounted at the same path — resource: paths always verify against the project root.

Upgrading to v0.6

1. Run fdf migrate on the bundle. From v0.5 nothing moves: the pin moves, SPEC.md is re-vendored, and practices/INDEX.md, debts/INDEX.md and a DOMAIN.md stub appear. One thing does change, and it is the point of the version — DOMAIN.md is a fifth Context document, so F9 holds the bundle to filling it before the next feature. fdf migrate itself never fails on that (fresh stubs are advisory); the next plain fdf validate does, until the fdf-init interview fills the lexicon. From v0.4 it also scaffolds changes/INDEX.md; from v0.2/v0.3 it additionally lifts nested trail files to stem-qualified siblings and scaffolds SURFACES.md.
2. Re-run fdf install for each harness you use. Skills and primers written under an older version do not know about practices/, debts/, the Practice and Debt types, or DOMAIN.md, and stay stale in CLAUDE.md/AGENTS.md until refreshed. fdf install upgrades skills automatically when the version marker changes; if your primer heading already exists with old wording, edit or replace that section.

Skills

fdf install places eight skills into your harness. Five walk a feature through its lifecycle; the other three are not stages at all — a router, a diagnostic front door, and a gate, each of which applies at every stage. An agent needs no prior FDF knowledge: fdf-help routes, and the spec is vendored in the bundle it is working in.

Skill	What it is for
fdf-help	The router. Finds the feature and its status, then sends the work to the right skill — before any code is written, including for "tiny" changes.
fdf-init	The project-context interview. Fills STACK / ARCHITECTURE / SURFACES / INFRA / DOMAIN with your approval, so every later feature is designed against what is actually true.
fdf-brainstorm	Idea → feature document. Questions the idea one at a time, writes the Gherkin, and gets your explicit design approval before writing slug.spec.md.
fdf-plan	Approved spec → executable plan. Tasks a zero-context implementer could run, plus slug.test.md: how each scenario will be proven.
fdf-execute	Plan → working code. Works tasks serially or in parallel batches, keeps statuses truthful, and will not call a feature done on an unrun test case.
fdf-change	Post-delivery writing. A Change when a delivered feature must behave differently; a Fix when the code drifted from what its document already says.
fdf-debug	Something is broken and nobody knows why yet. Finds the root cause first, then routes the repair — Fix, Change, new feature, or task work.
fdf-validate	The gate after every bundle edit. Turns fdf validate's rule codes into the honest fix, and refuses the fake ones (deleting a scenario so F8 stops asking).

The three human gates are: the Context interview (fdf-init), the design approval (fdf-brainstorm, and fdf-change for a Change), and any edit to a Context document. Everything between them is mechanical work an agent does on its own.

Common flows

Build a new capability

fdf-help → fdf-brainstorm → fdf-plan → fdf-execute

The spine. Brainstorm stops at "Do you approve this design?" and writes nothing before you say yes; plan turns the approved spec into tasks and the test document; execute works the tasks, flipping statuses as it goes, and reports the actual command output per test case. It ends by asking whether the work made any Context doc stale.

Fix a bug in a delivered feature

fdf-debug → (root cause) → fdf-change → fdf fix or fdf change

Debug first, because the root cause decides the document. Code contradicts a scenario that already exists → a Fix (no design gate; the lasting artifact is the regression case added to the feature's slug.test.md). No scenario covers the case, or the scenario itself is wrong → a Change, because someone now has to decide what should happen, and that needs the design gate.

Fix a bug in a feature still being built

fdf-debug → fdf-execute

A feature that has not shipped is repaired in place as task work. Change and Fix are only for done / retired features — F10 rejects anything else.

Change what a delivered feature does

fdf-help → fdf-change

A request, not a defect, so there is nothing to diagnose. The change declares its effects up front (add: / modify: / remove: per scenario), and F10 will not let it reach done until the feature's Gherkin actually says so.

Retire a capability

fdf-change → a Change with retires: and a # Rationale

The feature document is never deleted — it records behavior the software once had. The feature goes to retired, with replaced-by: when a successor exists.

Update ARCHITECTURE.md / INFRA.md after work that changed reality

fdf-execute / fdf-change → Context-doc review → your approval → LOG entry

Not a separate flow you start — it is the last step of the work that made the doc stale. The agent proposes the specific edit; nothing is written until you approve it, and the change is logged. If a Context doc is stale on its own, with no work in flight, re-run the fdf-init interview for that document.

Migrate infrastructure (new datastore, new deployment target)

First question: does anything a user or a calling system can observe change? — limits, error shapes, endpoints, auth, guarantees.

• Yes → every feature that promises that behavior gets a Change (fdf-change), or a new feature via fdf-brainstorm if the migration adds a capability. Then the INFRA.md / STACK.md update, approved and logged.
• No → the work is behavior-neutral, so no feature document changes. The only bundle artifact is the approved INFRA.md / STACK.md edit plus its LOG entry.

FDF has no document type for behavior-neutral engineering work, and deliberately so: the bundle records what the software does, not every task performed on it. Track the migration itself in your issue tracker.

Start a project, or adopt FDF in an existing one

fdf init → fdf-init → fdf-brainstorm

The interview is the most leveraged conversation in the whole workflow, and F9 blocks feature work until it is done — accurate context is what makes an agent build this project's way instead of guessing.

Spec

FDF is defined by versioned specs under spec/ — current v0.6, prior v0.5 / v0.4 / v0.3 / v0.2; SPEC.md indexes them. Each is normative for the bundles pinning its version, and every bundle vendors its pinned version's spec at docs/features/SPEC.md. testdata/ fixtures are the executable conformance contract. MIT licensed.

Documentation

Overview

Package fdf exposes the repo's skills and specs to the CLI.

Index

• Variables

Variables

var Assets embed.FS

Assets embeds the harness-neutral skills that `fdf install` places into an AI harness's configuration, and the versioned format specs (spec/<version>.md) that `fdf init`/`fdf migrate` vendor into a bundle's docs/features/SPEC.md.