einherjar/mcp

Every warrior who knew the sagas had a skald nearby. This is yours.

code.nochebuena.dev/einherjar/mcp is the Einherjar Model Context Protocol server. It is a remote, streamable-HTTP service that teaches AI assistants about every other module of the framework: which package exposes which type, what each module promises via its compliance tests, the canonical wiring shape for a service, and whether a snippet of Go follows the conventions. Anyone who works in an Einherjar codebase can point their AI tools at one URL and get answers grounded in the actual source.

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What Is Einherjar?

In Norse mythology, the Einherjar are the chosen warriors of Valhalla — selected not for glory, but to be ready for what comes after. They train. They prepare. They build the capability that others will rely on.

This framework is named for that purpose. Every module is a piece of that preparation: built carefully, documented for those who were never in the room, and designed to hold under pressure.

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Commands

Command	Purpose
cmd/server	Streamable-HTTP MCP server. Embeds the framework index at build time and serves it over a single HTTP endpoint.
cmd/indexer	Walks an Einherjar repository checkout and writes the framework index to data/index.json.

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Tools

The server exposes ten tools to MCP-aware clients (Claude desktop, Claude Code, Cursor, Zed, and anything else that speaks MCP):

Tool	Purpose
list_modules	Enumerate every Einherjar module with its purpose and sub-packages
get_module	Package doc, dependencies, sub-packages, key types, compliance counts; optional README
search_symbols	Find a type, function, or interface by name, doc text, sub-package, or module
get_symbol	Full signature, doc comment, and source location for one symbol
list_adrs	List architectural decision records, optionally restricted to one module
get_adr	Fetch a single ADR's markdown body
get_example	Canonical usage snippet — pulled from module READMEs and from the synthetic wire conventions
get_compliance	Interface assertions and structural test names from a module's compliance_test.go
get_changelog	Full CHANGELOG.md markdown for one module
validate_snippet	Pattern-match a Go snippet against framework conventions; returns findings with severity, hint, and line

validate_snippet ships eight wiring-convention rules at v0.1.0: launcher.missing-run, launcher.no-components, launcher.run-error-discarded, logz.direct-env-read, web.server-not-appended, wire.hook-bad-signature, wire.hook-outside-beforestart, and wire.route-specific-after-param.

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Build Flow

                  build time                          runtime
   ┌──────────────────────────────┐      ┌──────────────────────────┐
   │ cmd/indexer ../              │      │ cmd/server               │
   │   walks every Einherjar      │      │   streamable-HTTP MCP    │
   │   module, parses Go pkgs,    │ ──▶  │   tools served from the  │
   │   reads READMEs + ADRs       │      │   embedded index.json    │
   │   ⇒ data/index.json (embed)  │      │                          │
   └──────────────────────────────┘      └──────────────────────────┘

The indexer is a separate command. It produces data/index.json which the server embeds via //go:embed, so the deployed binary is self-contained and reads nothing from disk at runtime.

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Usage

Local run

# 1. Build the framework index from the sibling Einherjar modules
go run ./cmd/indexer ..

# 2. Build and run the server
go build -o bin/einherjar-mcp ./cmd/server
./bin/einherjar-mcp -addr :8080 -path /mcp

Container

# Build the image from the einherjar repo root so the indexer can walk every
# sibling module at image-build time.
docker build -f mcp/Dockerfile -t einherjar-mcp:0.1.0 .

docker run --rm -p 8080:8080 einherjar-mcp:0.1.0

Environment variables

Variable	Default	Effect
EINHERJAR_MCP_ADDR	:8080	Listen address for the MCP server
EINHERJAR_MCP_PATH	/mcp	HTTP path served by the streamable-HTTP endpoint

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Wiring Conventions (the synthetic wire module)

The MCP server ships a 15th, synthetic module called wire. It is not an Einherjar module — it documents the canonical application shape that uses Einherjar modules. The content lives at internal/index/builtins/README.md and is embedded at build time. AI assistants discover it via list_modules and read it via get_module and get_example the same way they read any real module.

The conventions captured: project layout (cmd/<app>/main.go, internal/wire/*.go, domain layout per feature), the fixed shape of Run(), the fixed shape of a with<Feature> hook (one lc.BeforeStart containing all construction and route registration), route-ordering rules for chi, the authz middleware helper, when to use skipPublicPaths vs skipMethodPath, and adapter patterns at the wire boundary.

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Dependency Rules

contracts  (zero dependencies)
    ↑
  core, web, auth, …                  (every framework module)
    ↑
   mcp                                (reads framework source at index-time only)

mcp imports nothing from other Einherjar modules at compile time. The indexer parses the framework source on disk and writes a JSON blob; the server embeds that blob. This keeps mcp outside the framework dependency graph: it can index any version of einherjar without versioning itself in lock-step.

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Verification

cd mcp/
go build ./...     # must compile clean
go vet ./...       # no warnings
go test ./...      # all tests pass
gofmt -l .         # no output

All four commands must produce clean output before a PR will be reviewed.

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Deployment

The server is a single self-contained static binary. There is no canonical hosting shape — pick whichever matches the rest of your infrastructure. Two patterns cover most cases:

• Container. The Dockerfile at the module root produces a distroless runtime image. Build from the einherjar repository root so the indexer can reach every sibling module at image-build time:

  docker build -f mcp/Dockerfile -t einherjar-mcp:0.1.0 .
  docker run --rm -p 8080:8080 einherjar-mcp:0.1.0
  

• Systemd / socket-activated binary. The server detects an inherited listener via github.com/coreos/go-systemd/v22/activation and uses it when present, falling back to -addr TCP binding otherwise. Same binary works in both modes — no flag, no env var. Drop the binary into /opt/<somewhere>/ and write a .socket + .service pair that matches your conventions.

Whatever shape you pick, the public-facing reverse proxy must keep response buffering off on the /mcp location. Streamable MCP delivers tool results via Server-Sent Events; default nginx, Envoy, or Caddy buffering batches the stream and breaks Claude's session before the first event arrives. For nginx that means proxy_buffering off; proxy_cache off; proxy_request_buffering off; chunked_transfer_encoding on; plus an extended proxy_read_timeout for long-lived sessions.

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Architecture Decisions

No ADRs at v0.1.0. The structural decisions in this release (synthetic wire module, go:embed of the index, build-time-not-runtime knowledge model, primitives not response shapes) are captured in the framework-wide memory and in this README.

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A blade is sharper when the warrior knows its name. This is what tells them.