Behavioral Contracts - Runtime behavior specifications

Catches What TypeScript Can't

TypeScript validates types, but can't catch unhandled API errors, missing rate limit handling, or edge cases.

// TypeScript: ✅ Types are fine
// Runtime: 💥 Unhandled error
const user = await axios.get('/api/user');

Source-Backed Claims

Every behavioral contract is backed by official documentation URLs. No opinions, only facts.

postcondition:
  throws: AxiosError
  required_handling: "..."
  source: https://axios-http.com/docs

AI-Friendly Output

Structured JSON output designed to feed directly to Claude or ChatGPT for automated fixes.

verify-cli --output violations.json
# Feed to AI agent
# Get automated fixes

100+ Package Contracts

Pre-built contracts for axios, prisma, stripe, openai, and 100+ more popular npm packages.

Open Source & Free

Fully open source under CC BY-SA 4.0 (corpus) and AGPL-3.0 (CLI). Free for all use. No vendor lock-in, no telemetry.

CI/CD Ready

Integrate into your build pipeline. Fail builds on critical violations before they reach production.

See It In Action

❌ Before

async function getUser(id: string) {
  // No error handling!
  const response = await axios.get(`/api/users/${id}`);
  return response.data;
}

✅ After

async function getUser(id: string) {
  try {
    const response = await axios.get(`/api/users/${id}`);
    return response.data;
  } catch (error) {
    if (axios.isAxiosError(error)) {
      if (error.response) {
        // Handle HTTP errors (4xx, 5xx)
      } else {
        // Handle network errors
      }
    }
    throw error;
  }
}

CLI Output:

❌ ERROR: axios.get() called without try-catch
   Location: src/api/users.ts:42:15
   Contract: axios@1.0.0 → get → network-failure postcondition
   Required: Check error.response exists before accessing properties
   Source: https://axios-http.com/docs/handling_errors