# mailchimp-mcp-server MCP Server

Mailchimp via MCP: draft, test, and send campaigns; manage audiences and subscribers; pull reports.

**Publisher claimed.** No tool list reported, and Pod has not connected to this server.

## Status

Pod has not dialled mailchimp-mcp-server yet, so everything on this page is what its publisher reported rather than what we observed. Registries describe servers; they do not connect to them. Until a check runs, treat the tool list below as a claim.

## Connect

Published as `@cyanheads/mailchimp-mcp-server` on npm. Runs locally.

## Known issues

**12 problems reported by people outside the maintainer team.** Issues filed by the project's own owners, members and collaborators are excluded — those are release checklists and internal refactors, not things that will go wrong for you. Showing 9.

### Most discussed

### docs(mailchimp_templates): tool description should state that per-section patching isn't supported and point to the campaign workflow

### Use case
Mailchimp's `PATCH /templates/{id}` only accepts `name`, `html`, `folder_id` — there is no way to update one section of a saved template. The tool description (`src/mcp-server/tools/definitions/mailchimp-templates.tool.ts:99-100`) doesn't say this, so LLMs asked to "change the headline in template X" either try to PATCH a partial HTML fragment (wrong result) or look for a `sections` field on this tool (doesn't exist). The real path for per-section edits is `mailchimp_campaigns` / `m

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/5) · 2026-04-21 · closed · 3 comments

### bug(templateSections): field has no usable description — LLMs can't construct correct per-section overrides

### Server version
0.2.6

### mcp-ts-core version
^0.6.3

### Runtime
Bun

### Transport
stdio

### Description
The `templateSections` field on the three campaign-content tools is typed `z.record(z.string(), z.unknown())` with either no describe or a one-liner that doesn't explain the contract. LLMs faced with a bare `Record<string, unknown>` guess — usually passing `{}`, inventing keys, or sending `null` values — and Mailchimp rejects with 400s like `{"errors":[{"field":"name","message":"Please

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/4) · 2026-04-21 · closed · 3 comments

### bug(schema): numeric IDs rejected when MCP client sends them as strings — use z.coerce.number() on all input-side numbers

### Server version
0.2.6

### mcp-ts-core version
^0.6.3

### Runtime
Bun

### Transport
stdio

### Description
Every input schema that takes a numeric ID, page count, or offset uses `z.number().int()` without `.coerce`. When an MCP client marshals those args as JSON strings (Claude Desktop, some bridges, and tool-use harnesses do this for int-shaped fields), the tool is rejected at input validation *before the handler runs*, with a message the user reads as a schema type mismatch:

```
MCP erro

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/3) · 2026-04-21 · closed · 1 comment

### bug: field-test round 2 — draft-report misreporting, swallowed upstream errors, UX carry-overs

### Server version

0.2.3

### mcp-ts-core version

^0.5.0

### Runtime

Bun

### Runtime version

Bun 1.3.x

### Transport

stdio

### Description

Second field-test pass against the live server (free-plan account, 1 audience, mix of drafts and sent campaigns). The `normalizeMailchimp()` refactor from #1 held up well and the three hard bugs from last round are gone. This pass surfaces two new bugs plus four UX findings — two of which are carry-overs from #1 that weren't in scope of that fix (U2

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/2) · 2026-04-20 · closed · 1 comment

### fix(config): pin MCP_SESSION_MODE to stateful — the image ships stateless and breaks the confirmation gate for v1 HTTP clients

`Dockerfile` sets `ENV MCP_SESSION_MODE="stateless"`, but `.env.example` carries a commented `# MCP_SESSION_MODE=stateful`, whose comment documents the value set as `stateful | stateless (default: stateful)`. The container and the same code run via `bunx`, `npm start`, or from source therefore resolve to different session modes.

For this server the container is the one that is wrong.

Related: cyanheads/mcp-ts-core#376

## Proposal

Settle every surface on `stateful`, and change the `Dockerfile

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/13) · 2026-08-22 · open · 0 comments

### Most recent

### bug(subscribers): validate email inputs before hashing member IDs

### Server version

0.3.7

### mcp-ts-core version

0.10.6

### Runtime

Bun

### Runtime version

Bun 1.3.11

### Transport

HTTP (Streamable HTTP)

### OS

macOS 15.x

### Description

Subscriber-address inputs are plain `z.string()` fields, so malformed emails pass local validation, get MD5-hashed into a Mailchimp member ID, and come back as an upstream 404. That makes a bad local input look like a missing subscriber.

### Steps to reproduce

1. Start the server with a valid `MAILCHIMP_API_KE

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/9) · 2026-07-02 · open · 0 comments

### bug(mailchimp_campaigns): description advertises invalid send-checklist operation

### Server version

0.3.7

### mcp-ts-core version

0.10.6

### Runtime

Bun

### Runtime version

Bun 1.3.11

### Transport

HTTP (Streamable HTTP)

### OS

macOS 15.x

### Description

`mailchimp_campaigns`'s top-level tool `description` lists campaign capabilities as "...replicate, content read/write, send-checklist, and RSS/resend controls" — phrasing that reads like an enumeration of operation values, since the preceding items in the same list (`list/get/create/update`, `replicate`) *are* r

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/8) · 2026-07-02 · open · 0 comments

### feat(responses): echo filters and add empty-result notice in structuredContent for list tools

### Use case

List-style tools (`mailchimp_campaigns`, `mailchimp_subscribers`, `mailchimp_audiences`, and other tools with a `list`-style operation) return a bare array in `structuredContent` with no echo of the filters that produced it and no actionable notice on zero results. The empty-state guidance that exists today lives only in `format()` prose (the `content[]` text block), which API clients and Claude Code don't read — they consume `structuredContent`. An agent that gets an empty list ha

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/7) · 2026-05-29 · open · 0 comments

### bug: field-test follow-ups — activity-feed crash, normalization leaks, UX fixes

### Server version

0.2.1

### mcp-ts-core version

^0.4.1

### Runtime

Bun

### Runtime version

Bun 1.3.11

### Transport

stdio

### OS

macOS 15.x (Darwin 25.1.0)

### Description

Full field-test pass against the live server (free-plan account, 1 audience, 6 pre-existing campaigns) surfaced one hard crash, two incorrect output fields, and a set of cross-cutting UX issues around response normalization. Filing as a single rollup so the related normalization work can be scoped together.

All 

[Read the thread](https://github.com/cyanheads/mailchimp-mcp-server/issues/1) · 2026-04-20 · closed · 0 comments

[See all 12 reports Pod holds for mailchimp-mcp-server](/mcp/mailchimp-mcp-server/issues).

## Firsthand observations

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