Config Validator — JSON & YAML Check
Validate JSON or YAML configuration structure checking for syntax errors, duplicate keys, and style issues.
How it works
- 1Paste or type your text in the input field
- 2Click "Validate" — processing happens in your browser
- 3Copy the result or download as a text file
What to do next
About Config Validator
Config Validator runs the developer utility job locally inside your browser. Validate JSON or YAML configuration structure checking for syntax errors, duplicate keys, and style issues. The work happens on your machine, the result is generated on your machine, and the page exposes the controls you need to drive it without burying them in menus.
Common audiences for Config Validator include data analysts wrangling JSON and backend developers inspecting requests, but plenty of people land on the page through a one-off search and never come back — that is also fine. The tool is built to be useful even when you only ever need it once.
Config Validator works well as a bookmarked utility you reach for when you need it. The first visit shows you what the tool does; the second is when you realise it is a low-friction option for the task and worth keeping in your tab list.
Config Validator runs on standard browser APIs — an open-source, well-audited engine that performs the developer utility natively in the browser. It accepts the formats listed in the upload area and produces output that opens in any standard developer viewer. Per-run input is capped at 0 MB.
Config Validator is structured so the question "where is my file processed?" has a single answer: in your browser tab. The engine, the controls, and the result panel are all on one page. Navigating away or closing the tab clears the page's memory the way it does for every other tab.
If your task needs more than one step, chain Config Validator with Env File Parser, Env to JSON Converter, and Firebase Config Validator. Each tool produces output that is a clean input to the next, so multi-step workflows are just a matter of opening the next tool in a new tab and continuing.
Constraints worth knowing about: inputs are capped at 0 MB to keep memory usage in a sensible range, one input is processed per run, and the tool must be loaded over HTTPS for the in-browser engine to work. These are properties of the architecture.
Config Validator is honest about scope: it handles a single, well-defined developer utility step. Specialist edge-case work — uncommon formats, very large inputs, or pipelines that need scripting — is what dedicated desktop apps are for. This page handles the common case quickly.
Output handling is intentionally boring: Config Validator produces a single output file and triggers your browser's standard "save" behaviour. If you have a default download folder configured, that is where it will land. There is no Favtoo-side history of jobs you have run.
Config Validator is one example of a broader pattern: utility software increasingly works as single-page, client-side experiences. Every page in the catalog is shaped that way, which keeps each tool fast to load and easy to recommend in a single link.
Config Validator runs as a regular web page, so there is no install step or permission grant before the first run. The page can be audited by viewing the source or by watching the developer-tools Network tab while a job runs.
Useful patterns when working with Config Validator: keep the input file open in another tab so you can compare against the result; give the output file a descriptive name when saving so you can find it later (the default name is sensible but generic); and treat each run as independent — the tool has no concept of "history", which means you cannot accidentally pollute one job with leftovers from another.
When something goes wrong, the cause is usually one of three things: a malformed input, a browser that is out of memory, or a corporate proxy that is interfering with the page's static assets. The first two are easy to diagnose; the third typically requires asking your IT team to allow standard browser APIs to load.
That is essentially everything Config Validator does and how it does it. Open the tool above, drop in your input, and the work happens in the page. If you find yourself reaching for it often, bookmark the page — it loads quickly on subsequent visits, and your most-recent settings are remembered for the rest of the session.
How it works
- 1Land on the Config Validator page. The tool is ready to use the moment the page renders.
- 2Drop a developer file onto the upload area, or click to pick one from your device.
- 3Adjust the options to match what you need. Sensible defaults cover the most common case, so you can usually skip this step.
- 4Hit the run button. standard browser APIs does the work in your browser tab.
- 5Download the result. The file is generated in your browser and saved through your normal download flow.
- 6Run additional jobs as needed. The same controls and defaults apply on every run.
Common use cases
- Inspect a payload during local development without writing a script using Config Validator.
- Convert between data formats while wiring up an integration.
- Encode binary content for transport in a JSON body.
- Pretty-print a minified blob during incident triage.
- Validate a config blob before pushing to staging.
- Decode a token to confirm its claims during a debugging session.
- Inspect a regex against a test string before committing it.
- Compare two API responses to spot a regression.
FAQ
Does it validate against a schema?
No — it checks structural validity and common style issues, not JSON Schema compliance.
YAML support?
YAML is checked for indentation consistency and tab usage, not fully parsed as YAML.
Duplicate keys?
JSON duplicate keys in the raw text are flagged; JSON.parse silently deduplicates.
Private?
Yes — validation runs in your browser.
TOML?
TOML is not supported in this version.
Large files?
Performance depends on browser capabilities; chunk very large configs if needed.
Can I use Config Validator offline?
Once the page is loaded, Config Validator can complete jobs without an active internet connection — the engine is bundled with the page, so there is no per-job network call. The initial page load does require a connection (to fetch the static assets), but after that you can disconnect entirely and the tool will still work. This is a side-effect of the local-first architecture, not a deliberate "offline mode" feature.
Will Config Validator keep working in a year?
Config Validator is updated whenever the underlying engine releases an improvement or a bug fix. Because the tool is delivered as a static page, every visit fetches the latest version automatically — there is no "version" to manage on your end. If a particular release ever changes default behaviour, the change is documented on Favtoo's changelog so you can confirm what shifted.
Can I trust the output of Config Validator for important work?
Config Validator is built on standard browser APIs, which is the same class of engine used by professional developer utility pipelines. For deterministic operations, the output is byte-identical to what an equivalent CLI run would produce; for operations involving a codec or a model, the result is well within the range of what comparable tools generate. If you have a specific reference output you need to match, run a small test job first to confirm the configuration produces what you expect.
What permissions does Config Validator need to function?
Config Validator only needs the standard web platform — file picker access for the inputs you choose to load, and optionally clipboard access if you copy the result rather than downloading it. There is no microphone, camera, geolocation or background-permission request, because none of those are needed for the work the tool does.
Will Config Validator ask me to pay to download the result?
Config Validator is free to use. The processing runs in your browser, which keeps the per-user cost low enough that the tool can be offered openly. The download is the same file the engine produced — you can use it for as many runs as you need.
How long does Config Validator take to process a file?
Most jobs finish in seconds. Speed scales with input size and with how many CPU cycles your browser tab has available — the engine runs in your browser, so it shares resources with whatever else you have open. For inputs near the 0 MB ceiling, expect anywhere from a few seconds to roughly a minute on a typical laptop. Closing other heavy tabs noticeably speeds things up.
What should I do if Config Validator fails on my file?
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is in a supported format and that it is below 0 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.
How is Config Validator different from desktop apps that do the same thing?
Desktop apps usually have more advanced features but require installation, maintenance and (often) a licence. Paid online tools are convenient but route your file through their servers and gate downloads behind accounts. Config Validator sits in between: free, instant, and private, but intentionally narrow in scope. For one-off jobs and the common developer utility operations, it is usually the lowest-friction choice; for highly specialised work, a dedicated app is still the right answer.