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mcp-zmq — MCP server for ZMQ messaging

PyPI Python Coverage Ruff

mcp-name: io.github.daedalus/mcp-zmq

Install

pip install mcp-zmq

Related MCP server: Sentinel-MCP

Usage

MCP Server

mcp-zmq

Python API

from mcp_zmq import zmq_publish, zmq_subscribe, zmq_send_request, zmq_listen_reply

Available Tools

  • zmq_publish: Publish a message to a ZMQ PUB socket

  • zmq_subscribe: Subscribe to messages from a ZMQ SUB socket

  • zmq_send_request: Send a request via ZMQ REQ socket

  • zmq_listen_reply: Listen for requests and reply via ZMQ REP socket

  • zmq_pair_connect: Connect to a ZMQ PAIR socket

  • zmq_pair_bind: Bind a ZMQ PAIR socket

  • zmq_status: Get ZMQ server status

Development

git clone https://github.com/daedalus/mcp-zmq.git
cd mcp-zmq
pip install -e ".[test]"

# run tests
pytest

# format
ruff format src/ tests/

# lint
ruff check src/ tests/

# type check
mypy src/

Available Tools

6 tools
zmq_listen_replyA

Listen for requests and reply via ZMQ REP socket.

ParametersJSON Schema
NameRequiredDescriptionDefault
bind_addressNoAddress to bind REP socket. Defaults to "tcp://127.0.0.1:5556".tcp://127.0.0.1:5556
reply_messageNoMessage to send in response to requests. Defaults to "OK".OK
timeout_msNoListen timeout in milliseconds. Defaults to 5000.

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

A3.7/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description must disclose behavioral traits. It does not mention that this tool blocks until a request is received, how timeout affects the behavior (e.g., returns null or throws), or whether concurrent requests are handled. This leaves critical execution semantics undocumented.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence that front-loads the core action ('Listen for requests and reply') and specifies the underlying protocol ('via ZMQ REP socket'). No unnecessary words; it is appropriately concise.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Although the input schema is fully covered and an output schema exists, the description omits important behavioral context such as the blocking nature of listening, timeout behavior, and error conditions. For a tool that modifies state (listens/replies), these gaps reduce completeness.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the input schema already documents all three parameters (bind_address, reply_message, timeout_ms) with defaults and descriptions. The description adds no additional semantic meaning beyond the schema, meeting the baseline expectation.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states that the tool listens for requests and replies using a ZMQ REP socket, which is a specific verb+resource pattern. It distinguishes from sibling tools like zmq_publish (PUB), zmq_subscribe (SUB), zmq_send_request (REQ), and zmq_pair (PAIR) by focusing on the REP/REQ pattern.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies this tool is for request-reply server-side usage but does not explicitly state when to avoid it (e.g., for one-way messaging) or mention prerequisites like ZMQ context initialization. However, the context is clear given the naming and sibling tools.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

zmq_pair_bindB

Bind a ZMQ PAIR socket for bi-directional communication.

ParametersJSON Schema
NameRequiredDescriptionDefault
bind_addressNoAddress to bind PAIR socket. Defaults to "tcp://127.0.0.1:5557".tcp://127.0.0.1:5557
messageNoOptional message to send after binding.
timeout_msNoTimeout in milliseconds. Defaults to 5000.

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

B3.1/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries full burden but only adds 'bi-directional communication' beyond the name. It does not disclose behaviors like blocking, error handling, or that binding creates a listening socket.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, concise sentence with no unnecessary words. It efficiently conveys the core action and purpose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool has an output schema (so return values need not be detailed) and 3 optional parameters, the description is minimalist. It lacks context about typical usage (e.g., binding as server-side) or interaction with siblings like zmq_pair_connect.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% with clear descriptions and defaults for all 3 parameters. The tool description adds no additional parameter meaning, but the schema already suffices, so baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Bind') and the resource ('ZMQ PAIR socket'), with the purpose ('for bi-directional communication'). It distinguishes from sibling tools like zmq_pair_connect, which connects instead of binds.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines1/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance is provided on when to use this tool versus alternatives like zmq_pair_connect, zmq_publish, etc. There is no mention of prerequisites, typical workflow, or scenarios where binding is appropriate.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

zmq_pair_connectB

Connect to a ZMQ PAIR socket for bi-directional communication.

ParametersJSON Schema
NameRequiredDescriptionDefault
connect_addressNoAddress to connect PAIR socket. Defaults to "tcp://127.0.0.1:5557".tcp://127.0.0.1:5557
messageNoOptional message to send after connecting.
timeout_msNoTimeout in milliseconds. Defaults to 5000.

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

B3.1/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries full burden but only states 'Connect' and 'bi-directional communication'. It fails to disclose blocking behavior, connection failure handling, state management, or disconnection procedures, leaving critical behavioral traits undocumented.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, concise sentence that is front-loaded. It is not verbose, but could potentially include more information without sacrificing conciseness, earning a 4.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool has three parameters (all documented), an output schema, and no annotations, the description lacks context about when to use it, prerequisites (e.g., need a bind endpoint), and behavior details like timeout handling, making it incomplete for an AI agent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so baseline is 3. The description does not add meaning beyond the schema's parameter descriptions, but it is acceptable as the schema already handles parameter semantics adequately.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Connect') and the resource ('ZMQ PAIR socket'), with the phrase 'bi-directional communication' distinguishing it from siblings like zmq_pair_bind (bind vs connect) and zmq_publish/zmq_subscribe (pub/sub pattern).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description does not provide guidance on when to use this tool versus alternatives such as zmq_pair_bind, nor does it explain that connecting requires a corresponding bind or the implications of using a PAIR pattern over others.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

zmq_publishB

Publish a message to a ZMQ PUB socket.

ParametersJSON Schema
NameRequiredDescriptionDefault
topicYesMessage topic/topic filter for subscribers.
messageYesMessage payload to publish.
bind_addressNoAddress to bind PUB socket. Defaults to "tcp://127.0.0.1:5555".tcp://127.0.0.1:5555

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

B3.1/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description must disclose behavioral traits like blocking, socket state requirements, or failure modes. It only states 'Publish a message', omitting whether the send is fire-and-forget or what happens if no subscribers are connected.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single concise sentence that gets to the point. It could benefit from slightly more context, but it is well-structured and front-loaded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Despite having an output schema and complete parameter coverage, the description leaves out important context such as whether the socket must already be bound or if the publish is synchronous. It is not sufficiently complete for an agent to confidently use the tool without additional knowledge.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, with each parameter already described (topic, message, bind_address with default). The description adds no additional meaning beyond the schema, so baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the verb 'publish' and resource 'message to a ZMQ PUB socket', which conveys the core purpose. However, it does not explicitly differentiate from sibling tools like zmq_send_request or zmq_subscribe, though the socket type 'PUB' hints at publish-subscribe pattern.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No explicit guidance on when to use this tool vs. alternatives such as zmq_subscribe or zmq_send_request. The socket type (PUB) implies a broadcast pattern, but the description does not articulate use cases or exclusions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

zmq_send_requestC

Send a request via ZMQ REQ socket.

ParametersJSON Schema
NameRequiredDescriptionDefault
messageYesRequest payload to send.
connect_addressNoAddress to connect REQ socket. Defaults to "tcp://127.0.0.1:5556".tcp://127.0.0.1:5556
timeout_msNoRequest timeout in milliseconds. Defaults to 5000.

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

C2.9/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description should fully disclose behavior. It only says 'send a request' but does not state that the REQ socket blocks until a reply is received, or that timeout_ms controls this wait. The existence of an output schema partially compensates for return value, but the blocking nature is critical and omitted.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single sentence, efficiently conveying the core action. It could include more detail without becoming verbose, so it is concise but not overly terse.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a messaging tool with 3 parameters and an output schema, the description is incomplete. It does not explain the request-reply pattern, the need for a listener, or the blocking behavior. The schema and output schema fill some gaps, but the high-level interaction model is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so each parameter is documented. The tool description adds only the context of 'via ZMQ REQ socket', which is marginally useful but not essential. Baseline 3 is appropriate as the description adds little beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the verb 'Send' and the resource 'a request via ZMQ REQ socket', which distinguishes it from siblings like zmq_listen_reply (listening) or zmq_publish (publish). However, it does not explicitly differentiate from other request-based tools or mention the one-shot nature.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool vs. alternatives. It does not mention that it requires a corresponding reply listener (e.g., zmq_listen_reply) or that it is for request-reply pattern only.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

zmq_subscribeB

Subscribe to messages from a ZMQ SUB socket.

ParametersJSON Schema
NameRequiredDescriptionDefault
topic_filterNoTopic to subscribe to. Empty string subscribes to all topics.
connect_addressNoAddress to connect SUB socket. Defaults to "tcp://127.0.0.1:5555".tcp://127.0.0.1:5555
timeout_msNoReceive timeout in milliseconds. Defaults to 5000.

Output Schema

ParametersJSON Schema
NameRequiredDescription

No output parameters

TDQS

B3.2/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of disclosing behavioral traits. It fails to mention whether the call blocks, handles timeouts, or requires persistent connections, leaving critical runtime behavior unspecified.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, focused sentence that immediately conveys the purpose. There is no extraneous information, and every word contributes to understanding.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Despite the presence of an output schema, the description lacks context about invocation behavior (e.g., blocking vs. non-blocking, message retrieval pattern) and does not compensate for the absence of annotations, leaving the definition incomplete for reliable tool selection.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3. The tool description adds no additional meaning beyond the schema's parameter descriptions, which are already informative.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the specific verb 'subscribe' and resource 'messages from a ZMQ SUB socket'. It effectively distinguishes this tool from its siblings (e.g., zmq_publish, zmq_send_request) by focusing on the subscription pattern.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance is provided on when to use this tool over alternatives, nor are there any prerequisites or context for use. The description only states the basic action, leaving the agent unaware of appropriate scenarios.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

TDQS

A3.6/5.0
Disambiguation5/5

Each tool targets a distinct ZMQ socket type or role (REP, PAIR bind/connect, PUB, REQ, SUB), with no overlap in purpose. Agents can clearly distinguish them.

Naming Consistency5/5

All tools follow a consistent zmq_verb_noun pattern using snake_case, making the naming predictable and uniform across the set.

Tool Count5/5

With 6 tools covering essential ZMQ socket types (REQ/REP, PUB/SUB, PAIR), the count is well-scoped and each tool serves a clear purpose.

Completeness4/5

The set covers fundamental ZMQ patterns but lacks support for PUSH/PULL, DEALER/ROUTER, and cleanup actions like disconnect. Minor gaps exist but core workflows are addressed.

Maintenance

ActivityInactive
ResponsivenessSyncing

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