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AI coding agents can produce working code that implements the wrong interpretation of a request. OpenSpec is a lightweight framework for making the intended behavior explicit, reviewing a proposed change before implementation, and keeping the resulting specification history connected to the work. Its key idea is to describe the difference a change should make—a delta—instead of rewriting the system’s entire specification.
What is OpenSpec?
OpenSpec is a framework for creating and managing software specifications so people and coding agents can stay aligned as a codebase changes. Its workflow connects a proposed change to requirements, implementation tasks, and an archive of completed work. The project describes its aim this way: “We help you refine the requirements, validate that they describe the right thing, and verify that the implementation matches.” (OpenSpec)
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OpenSpec does not make an AI agent infallible, and a specification is only useful if it accurately captures what the team wants. The practical benefit is a clearer, reviewable account of intent and change—not a guarantee of correct code or a measured improvement in reliability.
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A delta spec records proposed behavioral changes within an affected capability. It is distinct from the main specifications, which describe the system’s current behavior. This lets a change focus on what is new, altered, removed, or renamed rather than restating all known behavior.
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OpenSpec’s documented format uses four requirement operations:
- ADDED: introduces a requirement.
- MODIFIED: changes an existing requirement. Include the full updated requirement text so it can replace the old version during archiving.
- REMOVED: removes a requirement and includes a reason and migration guidance.
- RENAMED: changes a requirement’s name.
Each requirement should include at least one scenario in a WHEN/THEN form. These format rules make the intended behavior more concrete; they do not establish that the requirement is correct or that an implementation satisfies it. (OpenSpec schema documentation)
How do I use OpenSpec with AI coding agents?
The quickstart describes a five-stage cycle: Explore → Propose → Review → Apply → Archive. The example below is illustrative: imagine adding an option to save a user’s preferred display density.
1. Explore the codebase and the problem
Investigate the relevant behavior and discuss what the change should do before creating a plan. For the display-density example, clarify which settings are available, when the preference takes effect, and what should happen for existing users.
2. Propose the change
Ask the agent to draft a proposal, capability-specific delta spec, optional design notes, and a task list. The delta might specify that a selected density is saved and restored on the next visit, with scenarios describing the expected behavior.
3. Review before implementation
Read the proposed requirements and tasks before code is written. Check that the scope is right, the scenarios cover important cases, and the proposed behavior does not conflict with existing requirements. This is the point to correct a misunderstood request rather than discovering the mismatch only after implementation.
4. Apply the approved change
Have the agent work through the approved tasks. The workflow is intended to keep implementation tied to the change plan, rather than letting an open-ended prompt silently redefine the scope.
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5. Archive completed work
Once the change is complete, archive it so the main specs describe the system as built and the completed change folder remains available as history. The quickstart documents openspec archive for this lifecycle step. (OpenSpec quickstart)
What is the difference between validating requirements and verifying implementation?
These terms describe different checks. OpenSpec’s homepage frames validation as asking whether requirements describe the right thing, and verification as checking whether the implementation matches those requirements. In practice, separate three activities:
- Review intent: decide whether the agreed requirements express the behavior people actually want.
- Validate artifact structure: use
openspec validateto check OpenSpec changes and specs for structural issues. - Verify behavior: run appropriate tests or other checks to determine whether the software behaves as required.
The CLI’s validation command is documented as a structural check, not as comprehensive software test execution or formal proof of conformance. Use behavior-focused tests separately; the official materials do not claim that the command proves generated code is correct. (OpenSpec CLI documentation)
How does archiving preserve the specification and change history?
Archiving updates the main specification to reflect the completed behavior and moves the finished change folder into an archive. Added requirements are appended; modified requirements replace their earlier versions. The main specs therefore describe the system’s current behavior, while archived change artifacts preserve how a particular change was proposed and carried out. This division supports incremental work without losing the record of prior changes. (OpenSpec quickstart)
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A spec should make expected behavior observable enough to discuss and test. For each requirement, describe the triggering condition and the expected result in a WHEN/THEN scenario. Then review it for missing cases, ambiguous terms, and unintended scope before approving implementation.
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- State behavior rather than prescribing unnecessary implementation details.
- Include meaningful edge cases and existing-user behavior when relevant.
- For a modified requirement, provide the full replacement text rather than only a fragment.
- For a removed requirement, explain why it is removed and how users or dependent behavior should migrate.
- After implementation, use tests suited to the behavior; a structurally valid spec is not evidence that the software passes those tests.
These practices help connect intent to implementation, but the quality of the result still depends on the requirements, review, agent work, and independent checks.
When is a delta workflow useful—and what does it cost?
A delta workflow is most useful when a change touches existing behavior, multiple people or agents need a shared account of intent, or the team needs a traceable record of how requirements evolved. It makes more of the plan explicit than an informal prompt: requirements live in maintained files, review happens before implementation, and archived changes retain their history.
That structure also creates work. Someone must write or refine artifacts, review them, and keep the main specs useful as the software changes. The official materials do not quantify this overhead or establish that OpenSpec improves coding speed, defect rates, or agent reliability. For a small, low-risk one-off task, the added planning may not be worthwhile; for a change where misunderstanding is costly, a reviewable delta can make the work easier to coordinate.
Setup and compatible assistants
The OpenSpec homepage lists a range of compatible coding assistants, including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode, and Amazon Q Developer. This is the project’s compatibility directory, which may change; it is not a comparative assessment of assistant quality or evidence that integrations offer identical features. (OpenSpec compatibility directory)
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The homepage gives this global npm installation command:
npm install -g @fission-ai/openspec@latestAfter installation, initialize a project and follow the current quickstart to use OpenSpec through your assistant’s chat and CLI. Command behavior and schema details can change, so consult the current quickstart, CLI documentation, and homepage for the latest instructions.
As of October 7, 2026, OpenSpec’s homepage reported that it was used by more than 265,000 developers a month and that a new spec was created every two seconds. These are the project’s own live-site figures; the page does not provide methodology for independently auditing them. (OpenSpec)
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