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Configuration Reference

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hypen-code edited this page Mar 11, 2026 · 1 revision

Configuration Reference

MCE is configured entirely through environment variables (all prefixed MCE_) and a swaggers.yaml file. No config files are edited at runtime.

Environment Variables

General

Variable Default Description
MCE_LOG_LEVEL INFO Log verbosity: DEBUG, INFO, WARNING, ERROR
MCE_DEBUG false Enable debug mode (verbose output, stack traces)
MCE_HOST 0.0.0.0 Bind host for HTTP transport
MCE_PORT 8000 Port for HTTP transport

Compiler

Variable Default Description
MCE_COMPILE_ON_STARTUP true Automatically re-compile Swagger sources when the server starts
MCE_COMPILED_OUTPUT_DIR ./compiled Directory where compiled functions.py and manifests are written
MCE_SWAGGER_CONFIG_FILE ./config/swaggers.yaml Path to the Swagger source definitions file
MCE_LLM_ENHANCE false Send generated functions through an LLM to improve docstrings
MCE_LLM_MODEL gemini/gemini-2.0-flash LiteLLM model string: provider/model
MCE_LLM_API_KEY — API key for the LLM provider (required when MCE_LLM_ENHANCE=true)

Executor

Variable Default Description
MCE_LINT_ENABLED false Run ruff lint on generated code before sandbox execution
MCE_DOCKER_IMAGE mce-sandbox:latest Docker image for the execution sandbox
MCE_DOCKER_HOST — Docker socket path (e.g. unix:///var/run/docker.sock)
MCE_EXECUTION_TIMEOUT_SECONDS 30 Maximum wall-clock time allowed per execution
MCE_MAX_OUTPUT_SIZE_BYTES 1048576 Maximum sandbox stdout size (1 MB). Larger output is truncated.
MCE_NETWORK_MODE mce_network Docker network the sandbox container is attached to

Cache

Variable Default Description
MCE_CACHE_ENABLED true Enable the SQLite code cache
MCE_CACHE_TTL_SECONDS 3600 How long a cache entry lives before expiry (1 hour)
MCE_CACHE_MAX_ENTRIES 500 Maximum entries; oldest entries are evicted (LRU) when the limit is exceeded
MCE_CACHE_DB_PATH ./data/cache.db Path to the SQLite cache database file

Security

Variable Default Description
MCE_MAX_CODE_SIZE_BYTES 65536 Maximum code payload accepted (64 KB). Larger code is rejected before parsing.
MCE_ALLOWED_DOMAINS — Comma-separated list of allowed API hostnames. Empty = allow all. Example: api.weather.com,api.hotel.com

Per-Server Credentials

These are resolved at execution time and injected as Docker environment variables — they are never written to code or logs.

Variable pattern Description
MCE_{SERVER}_BASE_URL API base URL for this server
MCE_{SERVER}_AUTH Full auth header value, e.g. Authorization: Bearer sk-...
MCE_{SERVER}_EXTRA_HEADERS JSON object of custom headers, e.g. {"X-Version":"v1"}

{SERVER} is the uppercase version of the name field in swaggers.yaml. For a server named hotel_booking, the variables are MCE_HOTEL_BOOKING_BASE_URL, MCE_HOTEL_BOOKING_AUTH, etc.

Custom .env Files

By default MCE loads .env from the current working directory. Override with --env-file on any subcommand:

mce compile --env-file /path/to/.env.production
mce serve   --env-file /path/to/.env.staging
mce run     --env-file /path/to/.env.local
mce clean   --env-file /path/to/.env.local

Explicit environment variables always take precedence over values in the .env file.

Swagger Config (config/swaggers.yaml)

servers:
  - name: weather
    swagger_url: "https://api.weather.example.com/v1/openapi.json"
    base_url: "https://api.weather.example.com/v1"
    auth_header: "Bearer ${WEATHER_API_KEY}"   # ${VAR} resolves from env at runtime
    is_read_only: true                          # strips POST/PUT/PATCH/DELETE at compile time
    extra_headers:
      X-API-Version: "v1"
      X-Custom-Header: "value"

  - name: hotel_booking
    swagger_url: "./swaggers/hotel.yaml"        # local file path — relative to CWD
    base_url: "https://api.hotel.example.com/v2"
    auth_header: "Bearer ${HOTEL_API_TOKEN}"
    is_read_only: false

Field Reference

Field Required Type Description
name Yes string Unique identifier. Becomes the Python module name and the {SERVER} segment in env vars. Must be a valid Python identifier.
swagger_url Yes string HTTP(S) URL or local file path to the OpenAPI 3.x or Swagger 2.0 spec (JSON or YAML).
base_url Yes string API base URL. Injected at runtime via MCE_{SERVER}_BASE_URL; never exposed to LLMs.
auth_header No string Full authorization header. Use ${VAR} placeholders — never hardcode secrets. If omitted, no auth header is sent.
is_read_only No bool When true, MCE strips all endpoints with HTTP methods POST, PUT, PATCH, and DELETE at compile time. Default: false.
extra_headers No map Key-value pairs of custom HTTP headers added to every function call. Serialized to MCE_{SERVER}_EXTRA_HEADERS.

${VAR} Placeholder Resolution

Auth headers and extra header values can reference environment variables using ${VAR_NAME} syntax:

auth_header: "Bearer ${MY_API_TOKEN}"
extra_headers:
  X-Org-Id: "${MY_ORG_ID}"

These placeholders are resolved at runtime — not at compile time. The generated functions.py contains only os.environ references; the real values are injected via Docker environment variables when code executes.

LLM Enhancement

When MCE_LLM_ENHANCE=true, the compiler sends each generated functions.py through an LLM to improve docstrings and add usage examples. Credentials are not sent — only the code skeleton with os.environ[...] placeholders.

Requires the [llm] extra:

pip install -e ".[llm]"

Supported providers (via LiteLLM):

MCE_LLM_MODEL=openai/gpt-4o
MCE_LLM_MODEL=anthropic/claude-3-5-sonnet-20241022
MCE_LLM_MODEL=gemini/gemini-2.0-flash          # default
MCE_LLM_MODEL=openrouter/mistralai/mistral-7b-instruct

Complete .env.example 

# General
MCE_LOG_LEVEL=INFO
MCE_DEBUG=false

# HTTP transport (only used with --transport http)
MCE_HOST=0.0.0.0
MCE_PORT=8000

# Compiler
MCE_COMPILE_ON_STARTUP=true
MCE_COMPILED_OUTPUT_DIR=./compiled
MCE_SWAGGER_CONFIG_FILE=./config/swaggers.yaml
MCE_LLM_ENHANCE=false
# MCE_LLM_MODEL=gemini/gemini-2.0-flash
# MCE_LLM_API_KEY=your-llm-api-key

# Executor
MCE_LINT_ENABLED=false
MCE_DOCKER_IMAGE=mce-sandbox:latest
# MCE_DOCKER_HOST=unix:///var/run/docker.sock
MCE_EXECUTION_TIMEOUT_SECONDS=30
MCE_MAX_OUTPUT_SIZE_BYTES=1048576
MCE_NETWORK_MODE=mce_network

# Cache
MCE_CACHE_ENABLED=true
MCE_CACHE_TTL_SECONDS=3600
MCE_CACHE_MAX_ENTRIES=500
MCE_CACHE_DB_PATH=./data/cache.db

# Security
MCE_MAX_CODE_SIZE_BYTES=65536
# MCE_ALLOWED_DOMAINS=api.example.com,api.other.com

# Per-server credentials (replace MYAPI with your server name, uppercase)
MCE_MYAPI_BASE_URL=https://api.example.com/v1
MCE_MYAPI_AUTH=Authorization: Bearer YOUR_TOKEN_HERE
# MCE_MYAPI_EXTRA_HEADERS={"X-Version":"v1"}

Next: Security Model →

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