string.is

string.is is a lightweight, privacy‑first web service that performs deterministic conversions between string formats. At its core it exposes a single HTTP endpoint that accepts raw text and returns the transformed output in one of dozens of supported formats. The application is intentionally opinionated: it eschews cookies, enforces a strict Content Security Policy, and relies only on mature, well‑maintained dependencies. This makes it ideal for embedding in internal tooling or exposing as a micro‑service within a larger stack.

Technical Stack

The codebase is written entirely in TypeScript and runs on Node.js 20+. The server layer is powered by the Fastify framework, chosen for its minimal runtime overhead and excellent TypeScript support. Front‑end rendering is handled by React 18 with the Vite build system, providing fast hot‑reload during development and a highly optimized production bundle. All user input is parsed by the library layer (src/lib) which contains pure TS modules for identities, inputs, outputs, and converters. No React knowledge is required to extend this layer, enabling developers to add new conversions without touching the UI.

The application stores no state; all transformations are stateless and performed in memory. This eliminates the need for a database, simplifying deployment and scaling. When packaged with Docker, the image is built as a single‑layer Alpine container (~70 MiB) and exposes port 3000. Multi‑arch support (linux/amd64, linux/arm64) is baked in, allowing seamless deployment on modern cloud providers or edge platforms.

Core Capabilities

• Format Detection: Each identity module returns a confidence score (0–100) indicating how likely an input string matches a particular format. The server automatically selects the best identity to drive conversion.
• Extensible Converter Graph: Converters are composable input→output pairs. Adding a new converter involves creating an identity, an input parser, and an output formatter, then wiring them in src/lib/converters. The internal graph is discovered at startup, enabling automatic routing of conversion requests.
• API Surface: The public API is a single POST endpoint (/convert) that accepts JSON { input, from?, to? }. If from or to are omitted, the system infers them using identities and defaults. The response is a JSON payload containing { output, fromFormat, toFormat }.
• Webhooks & Callbacks: While not exposed out of the box, the architecture allows for hook registration via event emitters, enabling downstream services to react to conversion events.

Deployment & Infrastructure

string.is is designed for zero‑config self‑hosting. A single Docker image runs in a container or VM, and the only runtime dependency is Node.js (or the bundled binary). Scaling horizontally is trivial: multiple container instances behind a load balancer share identical stateless logic. The application logs to stdout, making it compatible with standard container logging solutions (e.g., CloudWatch, Loki). For environments that require isolation, the Docker image can be run in a dedicated namespace or with user‑specified resource limits.

Integration & Extensibility

The library layer is fully exported, allowing developers to import convert or individual converter classes into their own TypeScript projects. The identity, input, and output modules expose typed interfaces, facilitating static analysis and IDE autocomplete. Because the code is open source under an MIT license, contributors can fork, modify, or vend the library as part of larger tooling chains. The project also supports GitHub Actions for CI/CD, with linting (ESLint), testing (Jest), and code coverage (Codecov) integrated out of the box.

Developer Experience

Documentation is concise yet comprehensive: a single README explains architecture, usage patterns, and extension guidelines. The code follows strict linting rules and includes unit tests for every converter, ensuring reliability. Community support is active; issues are triaged quickly and pull requests merge promptly. The absence of cookies or analytics makes it a trustworthy choice for privacy‑conscious teams.

Use Cases

• CI/CD pipelines: Automate format validation and transformation (e.g., JSON to YAML) as part of build steps.
• Developer portals: Embed the tool in internal documentation sites to provide live conversion examples.
• Data migration scripts: Convert legacy string data between formats without writing custom parsers.
• API gateways: Expose a lightweight conversion endpoint that downstream services can call.

Advantages

• Performance: Fast, in‑memory processing with minimal dependencies leads to low latency (<10 ms for typical conversions).
• Flexibility: The modular converter graph allows adding new formats without redeploying the entire stack.
• Privacy: No cookies, no analytics, and a strict CSP make it safe for internal use or public exposure.
• Licensing: MIT license permits commercial use and redistribution without royalties.

In summary, string.is offers a developer‑centric, extensible platform for string format conversions that can be self‑hosted with minimal overhead and integrated seamlessly into modern development workflows.