Read, validate and refactor JSON Schemas — including private ones — without leaving VS Code.
Install · Documentation · Commands · CLI · Changelog
Per-feature demos are on the documentation site.
VS Code already validates JSON against a schema. This extension is for everything that starts after that:
| Built-in JSON/YAML support | JSON Schema Preview | |
|---|---|---|
| Validate JSON against a schema | ✅ | ✅ |
| Validate YAML, TOML and JSONL data | Partly (YAML via a separate extension) | ✅ |
| Schemas behind authentication | ❌ red squiggle, no IntelliSense | ✅ GitHub OAuth, Bearer, Basic |
| Read a schema as documentation | ❌ | ✅ live preview panel |
| Is this schema change breaking? | ❌ | ✅ classified diff + CI gate |
| Refactor a schema (extract, inline, rename) | ❌ | ✅ |
| Generate a schema from data, or types/data from a schema | ❌ | ✅ |
| Test a schema against pinned cases | ❌ | ✅ *.schema.test.json |
| Works headlessly in CI | ❌ | ✅ jstk CLI |
| Answers questions for your AI agent | ❌ | ✅ MCP + language model tools |
| Preview | Renders a schema as live, navigable HTML documentation in a side panel, scroll-synced with the editor. Ctrl+K V. |
| Outline | The Outline view, breadcrumbs and Go-to-Symbol show the schema's shape — properties, types, what's required — not the document's. |
$ref navigation |
Ctrl+click a $ref to jump to it; hover for a summary. |
$ref graph |
A bird's-eye diagram of which definitions reference which, and every external document pulled in. |
| Validate | JSON, JSONC, JSONL, YAML and TOML against a bound schema, with errors in the Problems panel and one-click quick fixes. |
| Lint | Schema-quality findings, including examples and defaults that contradict their own subschema — the bug no language server looks for. |
| Schema tests | Pin the documents a schema must accept and must reject in a *.schema.test.json file. Runs in the editor, in the workspace sweep, and in CI. |
| Workspace sweep | One command answers "is my repo green?" across data files, schema quality and schema contracts. |
| Diff & compatibility verdict | Classifies every change as breaking or not, against Git HEAD, a file or a URL — with a CodeLens showing the count while you edit. |
| CI gate | The same verdict headlessly: npx json-schema-toolkit diff old.json new.json --check --strict. |
| Refactor | Extract a subschema to $defs, inline a $ref, rename a definition across every reference, find all references, and delete definitions nothing uses. |
| Draft migration | Convert between draft-07, 2019-09 and 2020-12. |
| Schema from data | Infer a starting schema from a document you already have. |
| Data from schema | Valid sample instances — one, or many as a JSON array or JSONL. Every instance is validated before you see it. |
| Types from schema | TypeScript, Python, Go, Rust, Java, C#, Kotlin, Swift, Dart and C++. |
| Bundle / dereference | Flatten a multi-file schema into one self-contained document. |
| Private schemas | Authenticate against GitHub, Artifactory or any HTTPS endpoint — then cache the schema locally so VS Code's own language servers see it too. No more red squiggle. |
| Catalogs | Bind from SchemaStore or your own private catalog. |
| Offline | Falls back to the last cached copy when the network is unreachable, and says so. |
📖 Full feature list and command reference →
- Install from the Marketplace — or
ext install samdidos.json-schema-preview. - Open a JSON Schema and press Ctrl+K V to preview it.
- Open a data file, run JSON Schema: Bind Schema…, then Ctrl+K J to validate it.
A guided walkthrough opens on first install. Python is optional — the richer renderer uses json-schema-for-humans when it's available, and a built-in dependency-free renderer otherwise.
When a schema sits behind authentication, VS Code's language server can't fetch it — you get a red squiggle and IntelliSense goes dark. This extension authenticates on your behalf (GitHub OAuth, Bearer token, or Basic auth) and can cache the schema locally so the built-in language servers read it too.
Credentials go to your OS keychain via VS Code's Secret Storage, and are only ever sent to the host they were saved for.
The same core ships as a standalone CLI, json-schema-toolkit (command:
jstk) — validate, lint, diff with a compatibility gate, bundle, migrate, infer,
sample, and run schema tests, with no VS Code involved.
npx json-schema-toolkit diff api.v1.json api.v2.json --check --strict
npx json-schema-toolkit test contracts/*.schema.test.jsonAgents get schema questions wrong in exactly the places this project already answers them correctly — whether a change is breaking, whether a document validates. So the deterministic engines are exposed as tools, over two surfaces generated from one definition:
-
In VS Code — registered as language model tools, so any agent in the editor can call
validate,lint,diff,bundle,infer,sample,coverageandtestinstead of guessing. -
Anywhere else —
jstk mcpserves the same tools over MCP, so Claude Code, other IDEs, or a CI bot can use them too:
Optional AI-assisted authoring works the other way round: draft the descriptions your schema is missing, explain a validation error in plain language, draft a schema from a sentence, or generate realistic sample data.
It is off by default, and it never asks you for an API key: model access goes through VS Code's own Language Model API, so your configured provider does the work. Everything a model produces is put through this project's own engines — it must parse, compile under Ajv, lint clean, and be able to produce a valid instance — before it is offered, and nothing is written to a file without a preview.
All settings live under jsonschema.* (User, Workspace or Folder scope).
Customise the renderer with a .json-schema-preview-config.json in your
workspace root or the jsonschema.config setting — the file wins when both are
present.
- Zero telemetry — nothing about your usage is collected or transmitted, ever. There is no opt-in, because the capability isn't in the code.
- Hardened webviews — nonce-based CSP and HTML-escaped schema content in every panel.
- Offline-friendly — falls back to the last cached schema when the network is unreachable, and tells you it did.
- Accessible by default — every injected control is keyboard-operable and screen-reader-labelled; state is never colour-only.
Security & privacy guide → · Report a vulnerability
This project is spec-driven: every change traces to a requirement in
specs/, and npm run verify is the single gate that runs
locally and in CI. See CONTRIBUTING.md and
AGENTS.md — the latter is the guide for AI coding agents working on
this repo.
Engineering quality gates
Every requirement is traced to code and tests (matrix), and the project scores its own engineering maturity from observable facts (scorecard).
Rendering by json-schema-for-humans. Code generation by quicktype-core (Apache-2.0). Validation by Ajv.