Manifest error codes

When Manifest blocks or rejects a request, the response message starts with a code in square brackets:

[🦚 Manifest M100] No anthropic API key yet. Add one here: https://app.manifest.build/...
See https://manifest.build/docs/errors/M100

Look up the code below to see what it means and how to fix it.

Authentication (M001–M005)

These fire when the bearer token on /v1/chat/completions is missing or wrong. They surface as HTTP 401 to non-chat clients.

Code	What
M001: Missing Authorization header	No `Authorization` header on the request
M002: Empty Bearer token	Header present, token after `Bearer` is blank
M003: Invalid key format	Token doesn’t start with `mnfst_`
M004: Key expired	Key past its expiration date
M005: Key not recognized	No matching harness for this key

Providers (M100–M102)

Your Manifest key is fine, but provider credentials are missing or unusable. See Routing, API key providers, and Subscription-based providers.

Code	What
M100: Provider API key missing	Routing picked a provider you haven’t connected
M101: No providers configured	Harness has zero providers connected
M102: Provider subscription credentials unusable	Subscription OAuth/token exists but cannot be refreshed

Limits (M200–M204)

You hit a usage cap, rate limit, or Free plan request quota. M200-M203 surface as HTTP 429. M204 surfaces as HTTP 402 because it is a billing plan restriction.

Code	What
M200: Usage limit exceeded	Cost or message-count limit you set was crossed
M201: Per-user rate limit exceeded	More than 200 requests/minute from one user
M202: Per-IP rate limit exceeded	More than 500 requests/minute from one IP
M203: Concurrency limit exceeded	More than 10 in-flight requests at once
M204: Monthly request limit reached	Free plan monthly request quota was exhausted

Request validation and model selection (M300–M303)

M300 means the request body is malformed and surfaces as HTTP 400. M302 and M303 mean Manifest can’t reach the model the request asked for; both come back as a friendly proxy message.

Code	What
M300: Missing messages array	Body has no `messages` array, or it’s empty
M302: Model not available	Explicit model ID is not available for this harness
M303: Local provider unavailable on Manifest Cloud	Routed to Ollama, LM Studio, or llama.cpp on Cloud

M301 is missing from that list on purpose. It capped requests at 1000 messages, and the cap was removed. If an older self-hosted build still returns it, upgrade and the limit goes away.

Server (M500)

Manifest itself broke. Surfaces as HTTP 500.

Code	What
M500: Internal server error	Unhandled error in the proxy pipeline

Getting Started

Self-hosting

Features

Providers

Reference

Manifest error codes

Authentication (M001–M005)

Providers (M100–M102)

Limits (M200–M204)

Request validation and model selection (M300–M303)

Server (M500)

​Authentication (M001–M005)

​Providers (M100–M102)

​Limits (M200–M204)

​Request validation and model selection (M300–M303)

​Server (M500)

Authentication (M001–M005)

Providers (M100–M102)

Limits (M200–M204)

Request validation and model selection (M300–M303)

Server (M500)