Hooks are the part of Kiro that people underuse, mostly because the spec gets all the attention. But a hook that runs your test suite whenever the agent touches a service file catches broken output immediately, instead of at commit time when you have forgotten which change caused it.

What can a Kiro hook actually trigger on?

File save, file creation, and file modification events. You define the trigger, the file pattern it applies to, and the action. Actions can be agent instructions (“write a test for the newly added function”) or shell commands.

The file pattern is the important control. A hook scoped to src/api/** will not spam you when you tweak a README.

Which three hooks are worth setting up first?

1. Test runner: on modification of files under src/, run the test suite and report failures inline.
2. Docs updater: on creation of a new route or component file, append an entry to the docs index.
3. Style guard: on save, run the linter and let the agent fix formatting issues it introduced.

Start with the test runner. It is the cheapest hook to add and the one that prevents the most embarrassing bugs.

How do hooks compare to CI and pre-commit?

Hooks are not a replacement for CI. They are an earlier checkpoint. Think of them as the spell-checker: useful before you hit send, useless if you rely on it as your only editor.

What hooks should you avoid?

Anything slow. A hook that runs a full end-to-end suite on every save will make the agent feel frozen and you will disable it within a day. Keep hook actions under about 10 seconds; push anything heavier to CI.

Also avoid hooks that make autonomous changes without review. A hook that auto-commits to git is a footgun — keep commits manual.

Do hooks cost extra?

Hooks that invoke the agent consume the same request quota as normal agent actions. Shell-only hooks do not. So a test-runner hook using a shell command is effectively free, while a docs-updater hook that asks the agent to write text costs quota every time it fires. Design accordingly on the free tier.

Quick Summary

• Kiro hooks fire on file save, creation or modification and run an action.
• Scope hooks with file patterns to avoid noise.
• Start with a test runner hook scoped to your source folder.
• Keep hook actions fast; push heavy jobs to CI.
• Agent-backed hooks consume quota; shell hooks do not.

Most AI coding tools jump straight from prompt to files, which is why you end up with an app that works in the happy path and falls apart on the edges. Kiro inserts a document step: you approve what it will build before it builds it. That is the whole idea, and it is either exactly what you want or extra friction.

What is spec-driven development?

A spec is three files. Requirements list user stories with acceptance criteria. Design covers architecture and data models. Tasks break the design into ordered implementation steps. Kiro generates all three from your initial prompt, and you edit them like documents.

Once the spec is approved, the agent implements tasks and can run hooks — automated actions like updating docs or running tests — when files change.

How do you start your first Kiro project?

1. Install the Kiro app and sign in.
2. Create a new folder or open an empty project.
3. Describe the feature in plain language, including constraints like “no external database”.
4. Read the generated requirements and fix anything wrong. This is the important step.
5. Review the design and task list, then let the agent implement.
6. Check each diff; reject or refine tasks that drift from the spec.

Skipping step four defeats the purpose. If the spec says users can sign up with email but you also need SSO, your app will not have SSO.

Is Kiro free?

Kiro launched as a free preview and transitioned toward paid tiers with usage-based agent limits. New accounts typically get free requests per month, with higher limits on paid plans. Given how often this changes, confirm on the pricing page inside the app rather than trusting a blog post.

Where does Kiro fit vs prompt-first agents?

For a 30-line Python utility, writing a spec is wasted effort. For a feature that touches auth, billing and a database, the spec pays for itself the first time requirements change.

What are the drawbacks?

It is slower to start. You spend the first 20-30 minutes reading documents instead of seeing code. Some developers find the three-file structure rigid and end up maintaining docs that drift from reality once the agent starts improvising.

Also worth knowing: the initial preview was tied to a limited set of model options, which frustrated teams standardized elsewhere.

Good fit: developers building features with clear acceptance criteria, especially solo builders who want a paper trail. Bad fit: people who want instant output with zero ceremony.

Quick Summary

• Kiro is an AWS agentic IDE that writes a spec before writing code.
• Specs have three parts: requirements, design, tasks.
• Available on macOS, Windows and Linux with a free tier.
• Review and edit the requirements before approving implementation.
• Best for feature work with real requirements, overkill for quick scripts.