Build with Lexem.

From zero to a prompt fetched in your code — about five minutes.

1. 1

   Sign up and create a project

   Hit signup with email or Google. A “Personal” team is created automatically; rename it from Settings if you'll be inviting teammates. Then create a project from the dashboard.

2. 2

   Add a prompt and commit a version

   Open the project, click New prompt, name it, and write the prompt body in the editor. Add typed variables with {{name: string}} syntax. When you're happy, hitCommit — that snapshot is now an immutable version with an author, timestamp, and commit message.

3. 3

   (Optional) Promote to an environment

   Every project ships with dev, staging, and production environments. Click Environments on the project page, then Promote to deploy a specific version to dev. Promotion follows dev → staging → production; you can toggle approval-required on any environment column.

4. 4

   Generate an API key

   From the project page, click API keys → New API key. Save the lxm_... token shown — this is the only time you'll see it. Admins and Owners only.

5. 5

   Fetch it from your code

   TypeScript

   import { createClient } from "lexem-sdk";
   
   const lexem = createClient({ apiKey: process.env.LEXEM_API_KEY! });
   
   const p = await lexem.get("your-prompt-slug", { env: "production" });
   console.log(p.content);   // the prompt text
   console.log(p.versionId); // log this with your LLM call

   Pro tip

   Log versionId alongside every LLM call. When a regression appears in production, you'll know exactly which version of which prompt produced the output.

A handful of nouns power the entire product. Once these click, the UI navigates itself.

Project

A collection of prompts owned by a team. Permissions, environments, and API keys are scoped to a project.

Prompt & Version

A prompt is a named slot (e.g. summarizer). A version is an immutable snapshot of that prompt's content at a point in time, with a commit message and an author. You never overwrite a version — you commit a new one.

Branches & tags

Branches let you commit experimental variants without touching main. Merge a branch back to main when its eval score beats the incumbent. Tags (v1.0, stable,pre-launch) attach human-readable labels to specific versions.

Evals

An eval is a suite of test cases — each with input variables and an expected output — run against a prompt version. Three scorers are built in: exact match, regex, and LLM-as-judge. Lexem auto-flags regressions when a new version's score drops more than 5 points from the previous one.

Environments

Every project has three environments — dev, staging, production — seeded automatically. Each environment holds an active version per prompt. Promotion is strictly chained: a version must be live in dev before it can be promoted to staging, and live in staging before it can reach production. The order is enforced server-side.

Approvals

Toggle approval required on any environment column. With approval on, a promote click creates a pending Deployment that doesn't flip the active version until a teammate approves it from the Pending approvals panel at the top of the environments page.

API keys

Project-scoped bearer tokens (lxm_...) used by the SDK and REST API to fetch prompts. Generated by Admins, hashed at rest, shown once on creation, and revocable any time. lastUsedAt ticks with every successful auth so you can audit usage.

Team roles

Four tiers. Permissions stack — every tier inherits everything below it:

The official JavaScript / TypeScript SDK wraps the REST API with a small, typed surface, an in-memory cache, and a render() helper for variable interpolation. Requires Node 18+ (uses globalfetch).

Install

npm install lexem-sdk
# or
pnpm add lexem-sdk
# or
yarn add lexem-sdk

Create a client

import { createClient } from "lexem-sdk";

const lexem = createClient({
  apiKey: process.env.LEXEM_API_KEY!,
  baseUrl: "https://api.lexem.site",  // optional; default shown
  cacheTtlMs: 30_000,                  // optional; default 30s, 0 to disable
});

Get a prompt

const p = await lexem.get("summarizer", { env: "production" });
// {
//   content: "You are a helpful summarizer...",
//   versionId: "clxa...",
//   variables: [{ name: "article", type: "string", default: null }],
//   env: "production",
//   fetchedAt: "2026-05-17T08:00:00Z"
// }

Omit env to fetch the prompt's current main-branch head — useful in early development before you start promoting.

Render variables

const filled = await lexem.render(
  "summarizer",
  { article: "Q4 results showed..." },
  { env: "production" },
);
// returns the prompt string with {{article}} substituted

Missing variables throw by default. Pass { missing: "leave" } to keep placeholders, or { missing: "empty" } to substitute an empty string.

Caching

Results are cached in memory for 30 seconds per (slug, env) pair by default. Disable globally with cacheTtlMs: 0 in createClient, or bypass for a single call with fresh: true:

await lexem.get("summarizer", { env: "production", fresh: true });

// Or drop all entries (useful in tests):
lexem.clearCache();

Errors

import { LexemError } from "lexem-sdk";

try {
  await lexem.get("does-not-exist");
} catch (e) {
  if (e instanceof LexemError) {
    console.error(e.status, e.message);
    // 404, 'Prompt "does-not-exist" not found in this project.'
  }
}

If you're not on Node/TypeScript, hit the REST API directly. One public endpoint today — the same one the SDK calls.

Base URL

https://api.lexem.site

Authentication

Bearer token in the Authorization header. The key is the full lxm_... string from API keys.

curl https://api.lexem.site/v1/prompts/summarizer?env=production \
  -H "Authorization: Bearer lxm_your_key_here"

For quick debugging only, ?api_key= is also accepted as a query parameter. Don't use this in production — it ends up in access logs and browser history.

GET /v1/prompts/:slug

Fetches the active version of a prompt.

Query params:
  env   (optional)  Environment name: "dev", "staging", "production",
                    or any custom env. Omit to fetch the current
                    main-branch head.

Returns 200:
  {
    "content":    "You are a helpful summarizer...",
    "versionId":  "clxa...",
    "variables":  [{ "name": "article", "type": "string", "default": null }] | null,
    "env":        "production" | "current",
    "fetchedAt":  "2026-05-17T08:00:00Z"
  }

Errors:
  401  Missing or invalid API key (or key revoked).
  404  Prompt not found in this project, or no active version
       in the requested environment.

Lexem is open-source under MIT. Full setup instructions live in the repository README. The short version:

git clone https://github.com/rudra016/lexem
cd lexem
pnpm install
pnpm --filter @lexem/db migrate
pnpm dev

You'll need:

• Node 20.6+ and pnpm 9+
• A PostgreSQL database
• At least one provider API key (OpenAI / Anthropic / Google) to run evals or generate AI change summaries

When self-hosting, point the SDK at your deployment with baseUrl: "https://lexem.your-domain.com".