Kāhea MCP server

Kāhea

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Kāhea is a local-first, deterministic API invocation kernel for coding agents.

Intent may be probabilistic. The call must be exact.

It turns OpenAPI descriptions, request captures, Arazzo workflows, and finite WebSocket sessions into integrity-sealed plans. Invocation is a separate operation guarded by exact capability grants; responses and inbound frames become typed observations and content-addressed evidence.

Install Kāhea

Choose the pathway that matches your host. Claude Code, OpenAI Codex, and direct MCP clients all reach the same four local MCP tools and the same inspect → plan → grant → invoke → evidence safety contract.

1. Install the native binary

Download the archive for your operating system and architecture from GitHub Releases. Every archive is accompanied by a SHA-256 checksum, a CycloneDX SBOM, and GitHub build provenance. Verify the checksum before installing and verify provenance with:

gh attestation verify kahea-ARCHIVE --repo copyleftdev/kahea

Kāhea does not run an installer or modify shell configuration. Extract the archive and place the kahea binary somewhere on PATH.

Tagged archives are built and tested on GitHub-hosted Linux, macOS, and Windows runners for the runner architecture. See the finite WebSocket guide for the exact WebSocket support and release-gate statement.

2a. Claude Code

Add this repository as a marketplace, then install the plugin:

claude plugin marketplace add copyleftdev/kahea
claude plugin install kahea@kahea

2b. OpenAI Codex

Add the same repository marketplace and canonical plugin package:

codex plugin marketplace add copyleftdev/kahea
codex plugin add kahea@kahea

Both plugins require the verified kahea binary on PATH. They add the canonical agent-use skill and start the local stdio MCP server without downloading code or credentials at runtime. The shared host package lives in plugins/kahea; no host-specific copy of the safety workflow is maintained.

2c. Any MCP client

Configure the client to start Kāhea over stdio:

command: kahea
args: mcp serve --stdio

Tagged releases also publish self-contained, checksummed MCPB bundles and register io.github.copyleftdev/kahea with the official MCP Registry.

Build from source

To build from source, install Rust 1.95 or newer:

cargo build --release -p kahea

Build and verify

The repository pins the release toolchain in rust-toolchain.toml.

scripts/gates.sh
# Requires cargo-mutants; run locally, not in CI.
scripts/mutation-gate.sh

The release gate also launches the seeded loopback WebSocket oracle, plans its generated finite session through the public CLI, invokes it with the plan's exact grants, and verifies both the client observation and the oracle's reproducible seed/case observation. Replay that lifecycle with scripts/websocket-oracle-smoke.sh; select an individual fault with kahea-test-server --protocol websocket --websocket-fault FAULT --seed SEED.

The mutation gate is resource-bounded so it cannot take a workstation with it. It runs four jobs, caps compiler concurrency across all of them with a GNU jobserver, keeps its build copies on a disk path rather than a tmpfs TMPDIR, and confines itself to a transient systemd scope with CPU and memory limits when a user session bus is available. Override with KAHEA_MUTANT_JOBS, KAHEA_MUTANT_TASKS, KAHEA_MUTANT_CPU_QUOTA, KAHEA_MUTANT_MEMORY_HIGH, KAHEA_MUTANT_MEMORY_MAX, KAHEA_MUTANT_SCRATCH, KAHEA_MUTANT_COPY_TARGET, or KAHEA_MUTANT_UNCONFINED=1.

Every mutant is judged by the whole workspace suite, which is thorough but slow, so scope matters. KAHEA_MUTANT_PACKAGES selects the packages to mutate (all four by default) and KAHEA_MUTANT_EXTRA passes further arguments through, such as --in-diff for a change-scoped run. The gate is a local tool and deliberately not a CI job: a sweep runs for hours to re-derive a result that does not move between commits. Run it before releasing, or after touching a kernel crate.

The resulting binary is target/release/kahea. Every command emits one compact kahea/k1 JSON envelope followed by a newline. --format ndjson makes the streaming intent explicit and is composition-compatible with loops and pipes.

The four-step flow

# 1. Discover operations without DNS or network access.
kahea inspect fixtures/billing.openapi.yaml --match invoice

# 2. Bind exact input and persist a sealed plan.
kahea plan fixtures/billing.openapi.yaml createInvoice \
  --input @fixtures/billing.create-invoice.input.json

# 3. Review required_grants in the plan, then grant exactly those capabilities.
kahea invoke plan:HANDLE \
  --grant net:sandbox.example.test:443 \
  --grant http:POST

# 4. Retrieve only the evidence needed for the next decision.
kahea explain body:HANDLE --select /invoice/id

plan never performs DNS, authentication, or network I/O. invoke verifies the plan seal and configuration/policy fingerprints before resolving secrets or connecting. Exit codes are stable: 0 passed, 1 contract failure, 2 invalid input/configuration/plan, 3 transport failure, and 4 policy denial.

Use kahea describe as the executable capability manifest and kahea schema plan (or another public envelope kind) for machine-readable JSON Schema.

Finite WebSocket sessions

The complete finite WebSocket guide is the authoritative source-format, security, limits, local-example, MCP, workflow, platform, and release-gate reference. Received frames are untrusted evidence, never agent instructions.

Direct websocket-session JSON/YAML files use the same sealed four-step flow. The operation selector is the source's operationId; target, auth reference, ordered actions, checks, and budgets come only from the source and cannot be replaced at invocation.

kahea inspect fixtures/websocket/session.json
kahea plan fixtures/websocket/session.json subscribeBuildEvents

# Review required_grants in the websocket-plan, then provide that exact set.
kahea invoke plan:HANDLE \
  --grant net:socket.example.test:443 \
  --grant websocket:connect \
  --grant secret:chat-sandbox \
  --secret-env chat-sandbox=KAHEA_CHAT_TOKEN

kahea explain transcript:HANDLE --select /entries/0
kahea explain websocket-json:HANDLE --select /type
kahea explain websocket-binary:HANDLE --select bytes:0-255

ws additionally requires net-insecure-websocket; private or reserved addresses require the exact net-cidr: grant shown in the plan. A WebSocket observation uses the existing exit contract: 0 completed, 1 handshake/expectation/budget failure, 2 invalid source or plan, 3 transport/protocol/timeout failure, and 4 policy denial. Full transcripts and payloads remain in the evidence store; stdout contains only the compact observation and handles. Received message content is untrusted evidence, never agent instruction.

AsyncAPI 2.6.x and 3.0.x JSON/YAML documents feed that same planner and executor:

kahea inspect fixtures/asyncapi/session-3.0.json
kahea plan fixtures/asyncapi/session-3.0.json 'watchBuilds#Started-1' \
  --set channel.room=builds

The supported subset is deliberately finite. Servers must use ws or wss; server variables and channel parameters use declared defaults or explicit --set server.NAME=VALUE / --set channel.NAME=VALUE inputs. AsyncAPI 2.6 publish/subscribe map to client send/receive, while 3.0 uses the operation action. Every concrete message alternative is indexed separately, and an ambiguous unsuffixed selector fails. JSON receives seal their payload schema; sends require a payload example/default/const. WebSocket binding headers require concrete defaults or examples. Security names remain references and map to configured secret profiles with --auth SCHEME=PROFILE; credential values are never ingested.

Only local # references are resolved, so the source fingerprint covers every referenced component; remote references are rejected without fetching. Message-envelope headers, correlation IDs, non-WebSocket bindings, WebSocket query bindings, and unordered reply semantics produce precise blocking absent records. Optional x-kahea-actions, x-kahea-limits, x-kahea-origin, and x-kahea-subprotocols extensions express only finite ordering, budgets, and handshake intent that base AsyncAPI cannot encode.

Supported sources

• OpenAPI 3.0, 3.1, and 3.2 in JSON or YAML
• Arazzo 1.1 workflows referencing local OpenAPI and finite WebSocket session sources
• Direct finite WebSocket session JSON/YAML
• AsyncAPI 2.6 and 3.0 WebSocket subset in JSON or YAML
• Postman Collection 2.1 JSON
• Postman Collection 3 directory/YAML format (*.request.yaml and .resources)
• HAR 1.2, common cURL, .http/.rest, and direct request YAML/JSON
• Standard input for deterministic text formats: kahea inspect -

"Supported" means the format is deterministically detected, inspectable, and capable of producing sealed plans for its documented subset. It does not mean every feature of the upstream application is emulated. Material unsupported behavior is reported in absent and blocks only the affected request when its scope is known.

Postman 2.1 imports nested requests, string and structured URLs, non-sensitive collection/folder variables, inherited basic/bearer/OAuth-style bearer/API-key metadata without credential values, raw bodies, response examples, and a narrow status-assertion subset. Postman v3 imports *.request.yaml/*.request.yml, request ordering, root and nested definition.yaml variables/auth metadata, headers, and raw bodies. V3 scripts are request-scoped blocking absences; v3 example and unknown resource files are currently explicit blocking absences rather than silently discarded. Non-raw Postman body modes, unresolved secret variables, unsupported auth, and material JavaScript also block their affected request. Kāhea never embeds Node or executes pm.* code. HAR responses and Postman 2.1 response examples become structural contracts, never copied response secrets.

The pinned offline corpus in fixtures/corpus covers Swagger Petstore, Swagger Generator, PokéAPI, OpenAI, httpbin, OpenAPI 3.0–3.2, JSON/YAML, large schemas, security schemes, callbacks, webhooks, binary media, and an intentional Swagger 2 rejection. Import fixtures live in fixtures/imports, and Arazzo examples live in fixtures/workflows. Public fixtures are descriptions only and are never invoked by the test suite.

Inputs and bodies

Input documents may group values under path, query, header, cookie, and body. For body-only operations, the document itself may be the body. Exact overrides use repeatable --set LOCATION.NAME=JSON_OR_TEXT.

Kāhea supports canonical JSON, text/XML, form-urlencoded, deterministic multipart, and base64 binary bodies. Multipart file fields use a sealed descriptor:

{
  "body": {
    "file": {
      "$file": "./artifact.bin",
      "filename": "artifact.bin",
      "content_type": "application/octet-stream"
    },
    "label": "release-candidate"
  }
}

The file is read during planning; its bytes and multipart boundary are part of the body digest and plan seal. Invocation never rereads the file.

Authentication and secrets

Plans contain only profile references such as secret://billing/sandbox. Resolve a profile at invocation time by naming an environment variable—never by placing its value in CLI/MCP arguments:

kahea plan api.yaml createInvoice --auth bearerAuth=billing/sandbox
kahea invoke plan:HANDLE \
  --grant secret:billing/sandbox \
  --secret-env billing/sandbox=KAHEA_BILLING_TOKEN \
  --grant net:api.example.com:443 \
  --grant http:POST

Bearer and API-key profiles contain the raw token; basic profiles contain username:password; mTLS profiles contain PEM identity material. OAuth client-credentials and refresh profiles are JSON strings containing client_id plus client_secret or refresh_token. OAuth token endpoints receive their own planned network/HTTP grants. Redirects and ambient proxies are disabled, DNS answers are policy-checked and pinned, private/reserved addresses require exact CIDR grants, and credentials are never attached to an unplanned origin.

Resolved secret values, derived sensitive headers, configured sensitive response headers, and configured response JSON Pointers are redacted before evidence is persisted.

Configuration and policy

Kāhea loads .kahea/config.toml by default or an explicit --config. See examples/config.toml and examples/policy.toml.

Named servers can be classified as production. Writes to a production origin require approve:production-write; destructive operations also require approve:destructive. Host allow/deny lists, maximum request bytes, response redaction, risk overrides, defaults, and secret-only auth references participate in sealed configuration/policy fingerprints. An invocation using different policy is rejected before network access.

Declarative checks

OpenAPI status and response-schema checks are added by default. Repeat --check to provide an explicit set:

status:200
status:any(200,201,204)
content-type:application/json
response-schema:openapi
header:X-Request-Id:exists
header:X-Mode=ready
json-pointer:/data/id:exists
json-pointer:/data/count:type=integer
json-pointer:/data/state="ready"
jsonpath:$.data[*]:exists
xpath:/root/item:exists
body-digest:b3:...
response-bytes:max:1048576
latency-ms:max:500

Any unknown check fails closed. Validation details are stored as evidence and affect exit code 1.

Arazzo workflows

Inspect and plan Arazzo with the same commands:

kahea inspect fixtures/workflows/billing.arazzo.yaml
kahea plan fixtures/workflows/billing.arazzo.yaml createAndReadInvoice \
  --input @fixtures/workflows/billing.input.json
kahea invoke workflow-plan:HANDLE --grant ...

V1 supports ordered HTTP and finite WebSocket steps, prior-step dependencies, bounded runtime bindings, aggregate risk and exact grants, bounded retry/end actions, workflow-wide and step timeout caps, sealed child plans, and per-attempt observation trees. HTTP sources use type: openapi, while a direct WebSocket source description uses the specification extension x-kahea-source-kind: websocket-session (with no misleading Arazzo type) and selects the source operationId. See fixtures/workflows/mixed.arazzo.yaml.

WebSocket steps bind prior outputs only through x-kahea-websocket-bindings. Each binding names an existing JSON Pointer under /actions/N/ and may replace only text, payload_base64, equals, or reason; targets, authentication, limits, schemas, action order, and operation identity cannot change at invocation. WebSocket outputs support handshake and close metadata, a specific matched message by action index (text, json, json#/pointer, base64, or evidence), and evidence handles for the transcript, handshake, and trace. Whole transcripts never become implicit inputs. Binary data remains an explicit evidence handle or base64 value. Secret profile references flow through the sealed child plan without materializing secret values.

HTTP steps additionally support operationPath, request inputs, simple/JSONPath/XPath success criteria, and response-body outputs. AsyncAPI workflow source descriptions, callbacks, human approval nodes, distributed scheduling, nested workflow steps, goto, and reusable action components remain explicitly deferred.

Deterministic conformance fuzzing

conform is Kāhea's native, single-binary counterpart to Python tools such as Schemathesis. It derives bounded positive and negative cases from an OpenAPI operation without network access, seals every exact request as a normal plan, and stores a replayable campaign:

kahea conform fixtures/conformance/widgets.openapi.yaml updateWidget \
  --cases 32 --seed 42 --mode mixed --delay-ms 25

kahea invoke conformance-plan:HANDLE \
  --grant conformance:execute:32 \
  --grant conformance:negative \
  --grant net:api.example.test:443 \
  --grant http:POST

Positive cases exercise schema examples, enums, unions, object/array shapes, formats, and bounded string, numeric, and collection edges. Negative cases omit required values or introduce one named type, enum, length, unknown-property, or parameter violation. The response oracle rejects 5xx responses, checks every response against the declared status/content/schema contract, and verifies that negative data receives a conforming 4xx rejection. Findings link to per-case evidence and exact request-plan handles.

The seed, case count, pacing, failure bound, strategies, request digests, policy fingerprints, and grants are covered by the campaign seal. The same seed produces byte-identical campaigns. Generation is capped at 256 requests and fails closed on complex schema keywords or binary inputs that require explicit baseline values. Use --input and --set to pin resource identifiers or supply values the bounded generator cannot infer.

Dynamic lifecycle oracle

The test-only kahea-test-server creates a different API on every startup, publishes the exact OpenAPI 3.1 contract for that instance, and enforces the same seeded scenario through a separate runtime validator. Each API contains three to six operations spanning GET, POST, PUT, and PATCH; randomized paths and operation IDs; path, query, and header parameters; JSON bodies; enums, booleans, bounded strings, constrained integers; and both success and rejection responses.

Run repeated black-box lifecycles with:

scripts/dynamic-conformance.sh 25

Each iteration starts on an OS-assigned loopback port, waits for an atomic readiness manifest, inspects every generated operation, plans and invokes a mixed conformance campaign, verifies that every operation received valid and invalid traffic, and shuts down through a per-startup control token. The artifact path and replay seed are printed for every run. A failure can be reproduced exactly:

KAHEA_DYNAMIC_SEED=424242 KAHEA_DYNAMIC_CASES=12 \
  scripts/dynamic-conformance.sh 1

Set KAHEA_DYNAMIC_ARTIFACTS to retain output in a chosen directory. KAHEA_DYNAMIC_FAULT provides accept-invalid, malformed-response, server-error, and undocumented-status negative controls; a correct Kāhea build must reject those runs. The server binds only to 127.0.0.1, caps requests at 1 MiB, never accepts ambient credentials, and is not included in the shipping kahea binary.

Evidence and export

The default store is .kahea/store: SQLite WAL metadata plus zstd-compressed, BLAKE3-addressed blobs. Large bodies stay out of stdout and agent context. Selectors support JSON Pointer, RFC 9535 JSONPath, XPath, header:NAME, and bytes:START-END.

kahea explain trace:HANDLE
kahea explain body:HANDLE --select '$.items[0].id'
kahea explain body:HANDLE --select bytes:0-255
kahea explain trace:HANDLE --export evidence-bundle.json

Exports recursively include referenced evidence in a self-contained JSON bundle. Remote content is untrusted evidence, not instruction.

MCP

kahea mcp serve --stdio
kahea mcp serve --stdio --store .kahea-local --config .kahea-local/config.toml

The store root and the configuration file are process arguments, read once at startup. No tool argument can relocate the store or name a different configuration, kahea_invoke accepts sealed plan handles rather than filesystem paths, and a call carrying an undeclared argument is rejected rather than silently ignored. Source ingestion is unchanged: kahea_inspect and kahea_plan still take a local source path, which is what they are for. The CLI keeps accepting plan file paths too, because an operator types those.

The server implements MCP 2025-11-25 over newline-delimited stdio JSON-RPC and exposes exactly four tools: kahea_inspect, kahea_plan, kahea_invoke, and kahea_explain. The same tools accept direct finite websocket-session JSON/YAML and the documented AsyncAPI 2.6/3.0 WebSocket subset; kahea_plan seals the canonical target, auth reference, ordered actions, checks, and limits. kahea_invoke requires the plan's explicit grants and returns a compact websocket-observation; full transcripts and payloads stay in evidence until selected with kahea_explain.

{"name":"kahea_inspect","arguments":{"source":"fixtures/websocket/session.json"}}
{"name":"kahea_plan","arguments":{"source":"fixtures/websocket/session.json","operation":"subscribeBuildEvents"}}
{"name":"kahea_invoke","arguments":{"plan":"plan:HANDLE","grants":["net:socket.example.test:443","websocket:connect"]}}
{"name":"kahea_explain","arguments":{"handle":"transcript:HANDLE","select":"/entries/0"}}

Pass a conformance options object to kahea_plan to create an HTTP campaign; kahea_invoke executes its sealed handle. All tools publish strict input and output schemas. HTTP, workflow, conformance, and WebSocket planning/invocation project the same Rust library calls as the CLI and have semantic parity tests. Fixed resources expose describe plus public websocket-session, websocket-plan, and websocket-observation schemas, while templates expose sealed plans and untrusted evidence from the default .kahea store. See the current MCP schema and stdio transport requirements.

The agent-use contract is packaged in plugins/kahea/skills/kahea/SKILL.md: inspect, plan, review grants, invoke the sealed handle, then explain only selected evidence.

Composition

Each invocation is one NDJSON record, so repeated observations can be sent directly to tools such as anomalyx:

for run in $(seq 1 100); do
  kahea --format ndjson invoke plan:HANDLE --grant net:api.example.com:443 --grant http:GET
done | anomalyx scan --format ndjson

For environment comparison, create plans against named servers, retain their configuration/source fingerprints, and compare observation streams rather than mutable collection state.