# Spec-Driven Loop

> Run the same prompt against a fixed spec in a deterministic outer loop until the spec is satisfied.

- **Category**: Agentic AI
- **Subcategory**: Planning & Control Flow
- **Canonical URL**: https://designpattern.fyi/patterns/spec_driven_loop/

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## Description
**Intent**: Run the same prompt against a fixed spec in a deterministic outer loop until the spec is satisfied.
**Context**: A team works on a task with a clear or steadily-improvable specification — a long bug-fix list, a feature build that decomposes into small chunks, a migration whose end state is well-defined. Each iteration can move the codebase a little closer to the spec without trying to land everything at once. The team has a test suite or similar gate that can tell whether the spec has been satisfied.
**Solution**: - An outer shell loop (`while :; do cat PROMPT.md | claude-code; done`) runs the same prompt repeatedly. - The prompt encodes one task at a time, references a fix_plan.md that the agent itself updates, and ends with a test invocation that gates the next iteration. - Sub-agents are used for parallel reads; build/test stays serial.


## Use Cases
- A task has a clear (or improvable) spec and incremental iteration adds value.
- Each iteration's output can be gated by a test or check.
- An outer shell loop can run the same prompt repeatedly without supervision.





## Trade-offs


### Advantages

- Brutally simple; no orchestration framework required.

- Self-improving in practice as the agent updates the spec it learns.




### Considerations & Drawbacks

- Easy to burn tokens on the wrong shape if the spec is underspecified.

- Hard to share state between iterations beyond what the agent writes to disk.







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**Reference**: [Original Source](https://www.agentpatternscatalog.org/patterns/spec-driven-loop/)