dsh-resend-mcp

Resend email tools for DeepSeek Harness, wrapped as an installable DSH bundle.

Home: https://git.pvlb.dev/dsh-plugins/dsh-resend-mcp · Mirror: https://github.com/pvlb-dev/dsh-resend-mcp

The plugin connects to Resend's hosted MCP server (https://mcp.resend.com/mcp), resolves your API key from the DSH credential store, and exposes a curated subset of Resend's tools as native agent tools named mcp__resend__<tool>. A diagnostic resend_status tool reports the connection, credential reference, and active filter without revealing the key.

Not affiliated with Resend. Resend and the Resend logo are trademarks of their respective owners.

Status: v0.1.2 (same code as 0.1.0; documentation only), verified on 2026-10-22 against DSH 0.2.0-rc.2 and Resend's live MCP server: 9 tools registered from 137 available, and a test email was delivered from dsh@pvlb.dev to pvlb.dev@gmail.com. CI runs on Forgejo Actions; dsh-resend-mcp is published on npmjs and in the Forgejo registry.

What it looks like

One install command and one credential entry, and the model gets nine mcp__resend__* tools plus a diagnostic. Real output from resend_status on the reference deployment (DSH 0.2.0-rc.2, Resend MCP server 1.2.1):

Resend MCP: connected
Endpoint: https://mcp.resend.com/mcp
Namespace: resend
Preset: sending
Credential: RESEND_API_KEY (configured via file)
Tools: 9/137 registered
Registered: create-contact, get-contact, get-email, list-broadcasts,
            list-contacts, list-domains, list-emails, list-templates, send-email

The send path is verified end to end: a message sent from dsh@pvlb.dev reported delivered, and mcp__resend__get-email returned it by its Resend ID. mcp__resend__list-domains confirms the sending domain is verified with sending enabled.

Why a subset?

Resend's MCP server currently exposes 137 tools whose JSON schemas total roughly 405 KB — on every model request. Most sessions need a handful of them. This plugin selects a small, useful preset by default and lets you widen it explicitly:

Preset	Tools	Approx. schema size
minimal	send-email, list-emails, get-email, list-domains	~13 KB
sending (default)	minimal + list-contacts, get-contact, create-contact, list-templates, list-broadcasts	~26 KB
inbox	minimal + ten inbox read/thread/draft tools	~54 KB
full	every tool the server exposes	~405 KB today
custom	whatever tools matches	user-controlled

Requirements

• Node.js >= 22.6
• DSH >=0.2.0-rc.1 <0.3.0
• A Resend account with a verified sending domain and an API key
• pnpm available to the DSH Plugin Manager (the profile may need to name its absolute path)

Install

From npm (recommended)

dsh plugin --profile web add dsh-resend-mcp

The package is public: https://www.npmjs.com/package/dsh-resend-mcp. The DSH Plugin Manager resolves the plugin's DSH peers from the running installation; its own runtime dependency (@modelcontextprotocol/client) comes from npm.

From a checkout (development)

git clone https://git.pvlb.dev/dsh-plugins/dsh-resend-mcp.git
cd dsh-resend-mcp
npm run dev:link          # makes a local ("link:") install importable
dsh plugin --profile web add "$PWD"

npm run dev:link symlinks the DSH packages this plugin imports into the gitignored node_modules/. It is only needed for link: installs; a tarball or registry install gets its dependencies normally.

From a packed tarball

git clone https://git.pvlb.dev/dsh-plugins/dsh-resend-mcp.git
cd dsh-resend-mcp
npm pack
dsh plugin --profile web add ./dsh-resend-mcp-0.1.2.tgz

From the Forgejo registry

The Forgejo registry hosts the same version and is publicly readable, but npm still needs the dsh-plugins registry configured for that install; see docs/publishing.md. npm remains the one-command path.

After install, restart or reload the profile if the Plugin Manager reports restart-required.

Configure the API key

1. Create a key at https://resend.com/api-keys with permission to send email and read the resources you want the agent to use.

2. Add it to the local credential store, ~/.dsh/.credentials.yaml (or $DSH_HOME/.credentials.yaml), under the existing refs: map:

   refs:
     RESEND_API_KEY: re_your_api_key
   

   Add the entry; do not replace version, records, or other refs. The store watches the file and reloads it on change, so no restart is needed.

3. Keep the file owner-only. DSH refuses to load a credentials file that group or others can read; fix it with chmod 600 ~/.dsh/.credentials.yaml if necessary.

The key is resolved through ctx.credentials at connect time and never written to configuration, logs, tool output, or the repository.

This deployment's Web UI does not expose a generic credential editor, so editing the file (or exporting RESEND_API_KEY before launching DSH) is the supported path. The launching environment wins over the file: an exported variable shadows the stored entry and is reported read-only until you clear it.

To use a different credential reference, set apiKeyEnv in the plugin config.

Verify

Ask the agent to call resend_status, then list your domains:

Use resend_status to check the Resend connection, then call mcp__resend__list-domains.

A healthy result shows the credential as configured, the active preset, the registered tool names, and your verified domains.

Configuration

The bundle mounts with config: {}. Override fields through your profile's configuration layer when you need different behavior:

- id: dsh-resend-mcp
  name: dsh-resend-mcp
  config:
    preset: sending
    defaultSender: "you@example.com"

Field	Default	Description
serverName	resend	Namespace for mcp__<serverName>__<tool>
url	https://mcp.resend.com/mcp	Streamable HTTP MCP endpoint
apiKeyEnv	RESEND_API_KEY	Credential reference (never the value)
preset	sending	minimal, sending, inbox, full, or custom
tools	[]	Allowlist patterns; a non-empty list replaces the preset. * is a wildcard
excludeTools	[]	Patterns removed after the preset/allowlist
defaultSender	""	Verified sender address included in prompt guidance
toolCallTimeoutMs	60000	Per-tool-call timeout in milliseconds
startupTimeoutMs	30000	Initial connect and tool-list timeout
failOnStartupError	true	Fail activation instead of keeping resend_status with retries
maxInstructionBytes	8192	Bound on optional server instruction text

Examples:

# Only sending + email lookup
config:
  preset: minimal

# Everything, explicitly (large prompt prefix)
config:
  preset: full

# Add inbox reading on top of the default sending preset
config:
  preset: inbox

To use an explicit list, set tools; it replaces the preset:

config:
  tools:
    - send-email
    - list-emails
    - get-email
    - "*-domain"            # list-domains, get-domain, ...

Tools

All MCP-backed tools use the mcp__resend__ prefix and map 1:1 to Resend's server tools. The default sending preset exposes:

• mcp__resend__send-email
• mcp__resend__list-emails
• mcp__resend__get-email
• mcp__resend__list-domains
• mcp__resend__list-contacts
• mcp__resend__get-contact
• mcp__resend__create-contact
• mcp__resend__list-templates
• mcp__resend__list-broadcasts

Plus the native diagnostic:

• resend_status — connection state, credential reference/source, preset, registered tools, missing filter patterns, last error. It never prints the key.

Resend's send-email requires to, subject, text, from, context, and llm_model. The plugin's prompt guidance explains this and uses defaultSender when configured.

Security

• The API key is resolved from DSH credentials at connect/reconnect time.
• Configuration carries only the credential reference, never the value.
• Logs contain counts, names, and error messages — not headers or secrets.
• resend_status reports only whether the credential is configured and from which layer (file, env, …).
• The repository test suite includes a secret scan and fails on accidental re_… keys.

The credential store protects against accidental disclosure, not against a malicious agent running as the same OS user; see the DSH credentials documentation for that boundary.

Development

npm test             # unit tests, no network/DSH required
npm run check        # syntax checks + tests
npm run dev:link     # before a local-path install
npm run smoke        # real server check; needs RESEND_API_KEY in env
npm run pack:check   # inspect the publish artifact

scripts/smoke.mjs connects to the real server, prints the tool count and the selected names (not schemas), and can optionally send a test email with --send-to <address>.

See AGENTS.md for architecture, deployment facts, and the full verification checklist, TASKS.md for the backlog, and docs/publishing.md for CI, tagging, and registry setup (including the Forgejo npm registry).

Limitations

• Remote Streamable HTTP only; no stdio resend-mcp process and no OAuth browser flow.
• API-key bearer authentication only.
• DSH validates only its own JSON Schema subset locally. Resend keywords such as format, pattern, minItems, and maxItems reach the model but are enforced by Resend's server.
• Reconnection uses bounded exponential backoff; after the attempt budget the tools are unregistered until the plugin reloads or the Host restarts.
• No settings UI yet; configure through YAML.
• The plugin is installed profile-wide, affecting every session in that profile.

License

Apache-2.0. See LICENSE.