> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pre.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Fast vs Deep Specs

> Choose the right specification level for your project.

pre.dev offers two specification levels. The right choice depends on your project's complexity, timeline, and how much guidance you want build agents to have.

## Fast Spec (Plan)

**Structure:** Milestones → User Stories

A high-level spec that gives agents the big picture without granular subtask breakdowns. Agents figure out implementation details autonomously.

**Best for:**

* MVPs and prototypes
* Personal/side projects
* Rapid iteration workflows
* Solo developers
* Projects where speed matters more than detailed planning

**What you get:**

* High-level milestones with complexity estimates
* User stories for each feature
* Basic acceptance criteria
* Technical architecture overview

**Cost:** \~5-10 credits | **Speed:** \~30-60 seconds

## Deep Spec

**Structure:** Milestones → User Stories → Granular Subtasks

A comprehensive spec with implementation-level detail. Every task is broken down into specific, actionable subtasks with their own acceptance criteria.

**Best for:**

* Production applications
* Complex architectures
* Team coordination
* Mission-critical systems
* When you want maximum control over what agents build

**What you get:**

* Detailed milestones with phased delivery
* User stories with comprehensive acceptance criteria
* Granular implementation subtasks
* Task-level complexity estimates
* Detailed technical architecture with schema designs

**Cost:** \~10-50 credits | **Speed:** \~2-5 minutes

## Comparison

| Feature                | Fast Spec  | Deep Spec     |
| ---------------------- | ---------- | ------------- |
| Milestones             | Yes        | Yes           |
| User Stories           | Yes        | Yes           |
| Acceptance Criteria    | Basic      | Comprehensive |
| Granular Subtasks      | No         | Yes           |
| Architecture Depth     | Good       | Comprehensive |
| Effort Estimates       | High-level | Per-subtask   |
| Documentation Scraping | Yes        | Yes           |

## Decision Framework

**Use Fast Spec if:**

* You're validating an idea quickly
* The project is straightforward (CRUD apps, simple tools)
* You trust agents to make implementation decisions
* You want to iterate on the spec after seeing initial output

**Use Deep Spec if:**

* You're building something you'll ship to real users
* The project has complex business logic
* You want precise control over each implementation step
* You're working in a regulated domain (healthcare, finance)
* Multiple people need to understand the build plan

## Combining Both

<Tip>
  A common pattern is to start with a **Fast Spec** to validate the overall direction, then generate a **Deep Spec** once you're confident in the approach. The Deep Spec can reference the Fast Spec as context.
</Tip>

You can also generate a Fast Spec and selectively request deep breakdowns for only the complex milestones — keeping simple features at the story level while getting granular subtasks for the tricky parts.