Best API Checker Tools in 2026: Verify Your LLM API Endpoints

May 19, 2026 — Compare the top tools for detecting fake LLM models, token inflation, and API fraud.

If you are paying for API access to GPT-4, Claude, or Gemini through a reseller, you need an API checker. Here are the best tools to verify you are getting what you pay for.

Why You Need an API Checker

The API reselling market has serious problems: model substitution (GPT-3.5 sold as GPT-4), token inflation (counting 1000 tokens as 1500+), speed throttling, and relay chains that add latency and cost.

1. API-DNA (Free) ⭐ Recommended

API-DNA is the first dedicated API fingerprint verification engine. It provides deep scanning with 7-level trust scoring (L0-L7), provider fingerprinting for 30+ providers, evidence timeline, no signup required, and a CLI tool on npm.

2. Manual Header Inspection

Use curl to check response headers for proxy signatures, unusual Server headers, or missing X-Request-ID headers that indicate relay chains.

3. Token Counting Comparison

Use tiktoken to count tokens locally and compare with the API usage response. If the API consistently reports more tokens, you are experiencing token inflation.

4. Latency Profiling

Measure response times for your provider vs. the official API. Significant differences indicate relay chains or throttling.

How API-DNA Detects Fake APIs

1. Header Analysis — Examines server headers for proxy signatures
2. Token Format Validation — Checks API key prefixes
3. Model Behavior Testing — Analyzes response patterns
4. Latency Profiling — Compares response times
5. Model Family Detection — Verifies actual model
6. Provider Fingerprinting — Matches 30+ known providers
7. Trust Level Assignment — L0-L7 confidence score

Related: TokenC2C · SKILL.COFFEE