llm-katan 0.20.2

One tiny model, every LLM API. Drop-in test server for OpenAI, Anthropic, Bedrock, and Vertex.

LLM Katan

One tiny model, every LLM API. A lightweight server that exposes real provider API formats (OpenAI, Anthropic, Vertex AI, AWS Bedrock, Azure OpenAI) backed by a single local model or an echo backend. Built for testing AI gateways, API translation layers, and multi-provider routing without burning API keys or cloud credits.

Katan means "small" in Hebrew.

Features

• Multi-Provider — OpenAI, Anthropic, Vertex AI, AWS Bedrock (all 8 model families), Azure OpenAI
• Real Inference — runs actual tiny models (Qwen3-0.6B) via HuggingFace transformers or vLLM
• Echo Mode — instant startup, no model download, no GPU, no torch dependency
• Auth Validation — each provider requires its native auth header
• Streaming — all providers support SSE streaming in their native format
• Live Dashboard — real-time WebSocket-powered view of every request/response at /dashboard
• Prometheus Metrics — request counts, token usage, latency at /metrics
• Tool Calling — all providers accept tool definitions and return tool call responses in native format
• Multimodal — image content blocks accepted across all providers (OpenAI image_url, Anthropic image, Vertex inlineData, Bedrock image)
• JSON Mode — response_format: {type: "json_object"} returns valid JSON
• Failure Simulation — inject errors, latency, timeouts, and rate limits for gateway resilience testing
• 313+ Tests — extensive coverage for every provider, format, and edge case

Quick Start

pip install llm-katan

# Echo mode (instant, no dependencies)
llm-katan --model my-test-model --backend echo --providers openai,anthropic,vertexai,bedrock,azure_openai

# Real model (needs torch + transformers)
llm-katan --model Qwen/Qwen3-0.6B --providers openai,anthropic,vertexai,bedrock,azure_openai

Then open http://localhost:8000/dashboard to watch requests flow through in real-time.

How It Works

The server does not proxy to real providers. Each provider is a formatting layer around the same backend:

Request (any provider format)
       |
Provider (openai / anthropic / vertexai / bedrock / azure_openai)
  - Parses provider-specific request
  - Extracts: messages, max_tokens, temperature
       |
Backend (echo or real model)
  - Generates text (or echoes request metadata)
       |
Provider (same one)
  - Formats response in provider's native format
  - Returns to client

No translation chain, no SDK calls, no cloud API costs.

Supported Providers

OpenAI (--providers openai)

• POST /v1/chat/completions — Auth: Authorization: Bearer <key>
• GET /v1/models

Anthropic (--providers anthropic)

• POST /v1/messages — Auth: x-api-key: <key>

Vertex AI / Gemini (--providers vertexai)

• POST /v1beta/models/{model}:generateContent — Auth: Authorization: Bearer <token>
• POST /v1beta/models/{model}:streamGenerateContent

AWS Bedrock (--providers bedrock)

• POST /model/{modelId}/converse — Auth: Authorization: AWS4-HMAC-SHA256 <sig>
• POST /model/{modelId}/converse-stream
• POST /model/{modelId}/invoke — auto-detects model family:

Family	Model ID Prefix	Request Format
Anthropic Claude	anthropic.*	messages[], max_tokens, system
Amazon Nova	amazon.nova*	messages[].content[].text, inferenceConfig
Amazon Titan	amazon.titan*	inputText, textGenerationConfig
Meta Llama	meta.llama*	prompt, max_gen_len
Cohere Command	cohere.*	message, chat_history[]
Mistral	mistral.*	prompt, max_tokens
DeepSeek	deepseek.*	prompt, max_tokens
AI21 Jamba	ai21.*	messages[] (OpenAI-like)

Azure OpenAI (--providers azure_openai)

• POST /openai/deployments/{id}/chat/completions — Auth: api-key: <key>

Shared endpoints (no auth)

• GET / — server info
• GET /health — health check
• GET /metrics — Prometheus metrics
• GET /dashboard — live request/response dashboard
• GET /docs — Swagger UI

Example Requests

# OpenAI
curl -X POST http://localhost:8000/v1/chat/completions \
  -H "Authorization: Bearer test-key" \
  -H "Content-Type: application/json" \
  -d '{"model":"gpt-4o","messages":[{"role":"user","content":"Hello"}]}'

# Anthropic
curl -X POST http://localhost:8000/v1/messages \
  -H "x-api-key: test-key" \
  -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{"model":"claude-sonnet","max_tokens":100,"messages":[{"role":"user","content":"Hello"}]}'

# Vertex AI
curl -X POST http://localhost:8000/v1beta/models/gemini-pro:generateContent \
  -H "Authorization: Bearer test-token" \
  -H "Content-Type: application/json" \
  -d '{"contents":[{"role":"user","parts":[{"text":"Hello"}]}]}'

# Bedrock Converse
curl -X POST http://localhost:8000/model/anthropic.claude-v2/converse \
  -H "Authorization: AWS4-HMAC-SHA256 Credential=test" \
  -H "Content-Type: application/json" \
  -d '{"messages":[{"role":"user","content":[{"text":"Hello"}]}]}'

# Azure OpenAI
curl -X POST "http://localhost:8000/openai/deployments/gpt-4/chat/completions?api-version=2024-10-21" \
  -H "api-key: test-key" \
  -H "Content-Type: application/json" \
  -d '{"messages":[{"role":"user","content":"Hello"}]}'

CLI Options

llm-katan [OPTIONS]

Required:
  -m, --model TEXT              Model name (or any string in echo mode)

Optional:
  -b, --backend [transformers|vllm|echo]  Backend (default: transformers)
  --providers TEXT              Comma-separated providers (default: openai)
  -p, --port INTEGER            Port (default: 8000)
  -n, --served-model-name TEXT  Model name in API responses
  --max-tokens INTEGER          Max tokens (default: 512)
  -t, --temperature FLOAT       Temperature (default: 0.7)
  -d, --device [auto|cpu|cuda]  Device (default: auto)
  --quantize/--no-quantize      CPU int8 quantization (default: enabled)
  --max-concurrent INTEGER      Concurrent requests (default: 1)
  --tls                         Enable HTTPS with self-signed cert
  --tls-cert PATH               Custom TLS certificate (use with --tls-key)
  --tls-key PATH                Custom TLS private key
  --validate-keys               Enforce API key validation
  --api-keys TEXT               Override keys: openai=mykey,anthropic=mykey2
  --stats-file PATH             Persistent stats file (default: ~/.llm-katan/stats.json)
  --log-level [debug|info|warning|error]  Log level (default: INFO)

Failure Simulation (echo backend only):
  --error-rate FLOAT            Probability (0.0-1.0) of returning HTTP 500 (default: 0.0)
  --latency-ms INTEGER          Artificial delay per response in ms (default: 0)
  --timeout-after INTEGER       Return 504 after N successful requests (default: 0 = disabled)
  --rate-limit-after INTEGER    Return 429 after N requests (default: 0 = disabled)

Tool Calling

When tools are included in a request, the simulator returns a tool call response using the first tool with dummy arguments generated from its parameter schema. This lets you test API translation pipelines that need to handle tool calling across providers.

# OpenAI — returns tool_calls with finish_reason: "tool_calls"
curl -X POST http://localhost:8000/v1/chat/completions \
  -H "Authorization: Bearer test-key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "test",
    "messages": [{"role": "user", "content": "What is the weather in SF?"}],
    "tools": [{"type": "function", "function": {
      "name": "get_weather",
      "parameters": {"type": "object", "properties": {"location": {"type": "string"}}}
    }}]
  }'

# Anthropic — returns content block with type: "tool_use", stop_reason: "tool_use"
curl -X POST http://localhost:8000/v1/messages \
  -H "x-api-key: test-key" -H "anthropic-version: 2023-06-01" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "test", "max_tokens": 100,
    "messages": [{"role": "user", "content": "Weather in SF?"}],
    "tools": [{"name": "get_weather", "input_schema": {
      "type": "object", "properties": {"location": {"type": "string"}}
    }}]
  }'

Each provider uses its native tool calling format:

Provider	Request field	Response format	Stop reason
OpenAI	tools[].function	message.tool_calls[]	tool_calls
Anthropic	tools[].input_schema	content[{type: "tool_use"}]	tool_use
Vertex AI	tools[].functionDeclarations	parts[{functionCall}]	STOP
Bedrock	toolConfig.tools[].toolSpec	content[{toolUse}]	tool_use
Azure	tools[].function	message.tool_calls[]	tool_calls

Tool result messages (role: "tool" in OpenAI, tool_result blocks in Anthropic, functionResponse in Vertex, toolResult in Bedrock) are accepted in follow-up requests.

Multimodal

Image content blocks are accepted in all providers. In echo mode, images are described as [image:mime/type] in the response without processing the actual image data.

# OpenAI — image_url content blocks
curl -X POST http://localhost:8000/v1/chat/completions \
  -H "Authorization: Bearer test-key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "test",
    "messages": [{"role": "user", "content": [
      {"type": "text", "text": "What is in this image?"},
      {"type": "image_url", "image_url": {"url": "data:image/png;base64,iVBOR..."}}
    ]}]
  }'

Provider	Image format	Echo output
OpenAI / Azure	{type: "image_url", image_url: {url}}	[image:image/png]
Anthropic	{type: "image", source: {media_type, data}}	[image:image/png]
Vertex AI	{inlineData: {mimeType, data}}	[image:image/jpeg]
Bedrock	{image: {source: {format, bytes}}}	[image:png]

Failure Simulation

When testing AI gateways and load balancers, you need to verify they handle provider failures correctly — retries, failover, circuit breaking. These flags let you simulate real-world failure modes without touching a real provider:

# 30% of requests fail with HTTP 500
llm-katan -m test --backend echo --error-rate 0.3 --providers openai

# Every response takes 2 seconds (simulates a slow provider)
llm-katan -m test --backend echo --latency-ms 2000 --providers openai

# Works fine for 100 requests, then goes down (504)
llm-katan -m test --backend echo --timeout-after 100 --providers openai

# Works fine for 50 requests, then rate-limits (429)
llm-katan -m test --backend echo --rate-limit-after 50 --providers openai

# Combine: slow + flaky
llm-katan -m test --backend echo --latency-ms 500 --error-rate 0.1 --providers openai

Errors are returned in each provider's native error format — an OpenAI 429 looks different from a Bedrock 429 or an Anthropic 429, just like the real providers. The request counter for --timeout-after and --rate-limit-after is shared across all providers on the same instance.

Example use case: Run two llm-katan instances — one healthy, one with --error-rate 0.3. Point your AI gateway at both and verify it detects the degraded instance and shifts traffic to the healthy one.

Development

git clone https://github.com/yossiovadia/llm-katan.git
cd llm-katan
pip install -e ".[dev]"
pytest tests/ -v

License

Apache-2.0

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Created by Yossi Ovadia

Contributors

• Noy Itzikowitz