FIFO mcp

Connect your assistant to mkfifo.com

This FIFO is the MCP endpoint of mkfifo.com: https://mkfifo.com/mcp. An assistant that speaks the Model Context Protocol, for example Claude Code, connects to it with no account and no key. In Claude Code, run claude mcp add --transport http mkfifo https://mkfifo.com/mcp. Other assistants take the same URL, as a server of the type http.

The endpoint has one tool, run. It runs a script of the FIFO shell, the same shell as the terminal and https://mkfifo.com//bin/sh, and gives its output. So an assistant can use the builtins, such as jq, sed and sha256sum, and send Requests to FIFOs with a pipe: printf %s "$data" | my-fifo. A script cannot reach the FIFOs of a home, and it gets no key of this FIFO.

Each request of the assistant is a Request to this FIFO, and the envelopes below are its rules. Each case of the protocol is one ingress envelope: the methods tools/list and tools/call, the first request initialize of an older client, and each error. A jq command in each answer writes the JSON-RPC reply. You can read the envelopes, but you cannot change them. mkfifo.com keeps nothing of the requests.

Egress envelopes of ingress envelope 1

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-700b-80bd-1ff051bbb04c@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c --arg out "$(eval $script 2>&1)" '{jsonrpc: "2.0", id: .id, result: {resultType: "complete", _meta: {"io.modelcontextprotocol/serverInfo":{"name":"mkfifo.com","title":"mkfifo.com","version":"1"}}, content: [{type: "text", text: $out}], isError: ($out | startswith("eval: "))}}')

Show the body Show the header

The tool run, for a client of an older version of MCP: its request has no version in _meta.

Egress envelopes of ingress envelope 2

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7013-a203-a7f120b1141e@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c --arg out "$(eval $script 2>&1)" '{jsonrpc: "2.0", id: .id, result: {resultType: "complete", _meta: {"io.modelcontextprotocol/serverInfo":{"name":"mkfifo.com","title":"mkfifo.com","version":"1"}}, content: [{type: "text", text: $out}], isError: ($out | startswith("eval: "))}}')

Show the body Show the header

tools/list: one tool, run, with the schema of its input. The client can keep the list for one hour.

Egress envelopes of ingress envelope 3

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-701b-8252-946644038bcd@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, result: ({resultType: "complete", _meta: {"io.modelcontextprotocol/serverInfo":{"name":"mkfifo.com","title":"mkfifo.com","version":"1"}}} + {"tools":[{"name":"run","title":"Run a script of the FIFO shell","description":"Runs a script of the FIFO shell of mkfifo.com, as https://mkfifo.com//bin/sh does, and gives its output. The shell has the builtins of mkfifo.com with the options of the usual tools: printf, echo, cat, head, tail, cut, tr, wc, grep, sed, sort, uniq, xargs, jq, base64, basenc, sha256sum, md5sum, hmac, date, random, uuidgen, gzip, gunzip, zstd, markdown, ls, lsjson, sh and eval. Pipes, $( ), variables (name=value) and the redirections <, >, >>, 2> and 2>&1 work as in sh. A FIFO is a named pipe: printf %s \"$data\" | my-fifo sends a Request to the FIFO my-fifo and gives its answer, printf hi > my-fifo sends a Request with no output, and jq . < my-fifo reads the answer of a GET. ls my-fifo and cat my-fifo/PATH read the files of a FIFO. There is no ||, $?, here-document or backquote. A script stops at its first error, and the error is the result. A script cannot reach the FIFOs of a home. Each call is one Request to mkfifo.com, with its limits: 1 MiB of output, and the work of one Request.","inputSchema":{"type":"object","properties":{"script":{"type":"string","description":"The script, one command or more, one on each line."}},"required":["script"],"additionalProperties":false},"annotations":{"readOnlyHint":false,"destructiveHint":false,"openWorldHint":true}}],"ttlMs":3600000,"cacheScope":"public"})}')

Show the body Show the header

tools/list, for a client of an older version.

Egress envelopes of ingress envelope 4

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7023-ae43-ee0086435040@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, result: ({resultType: "complete", _meta: {"io.modelcontextprotocol/serverInfo":{"name":"mkfifo.com","title":"mkfifo.com","version":"1"}}} + {"tools":[{"name":"run","title":"Run a script of the FIFO shell","description":"Runs a script of the FIFO shell of mkfifo.com, as https://mkfifo.com//bin/sh does, and gives its output. The shell has the builtins of mkfifo.com with the options of the usual tools: printf, echo, cat, head, tail, cut, tr, wc, grep, sed, sort, uniq, xargs, jq, base64, basenc, sha256sum, md5sum, hmac, date, random, uuidgen, gzip, gunzip, zstd, markdown, ls, lsjson, sh and eval. Pipes, $( ), variables (name=value) and the redirections <, >, >>, 2> and 2>&1 work as in sh. A FIFO is a named pipe: printf %s \"$data\" | my-fifo sends a Request to the FIFO my-fifo and gives its answer, printf hi > my-fifo sends a Request with no output, and jq . < my-fifo reads the answer of a GET. ls my-fifo and cat my-fifo/PATH read the files of a FIFO. There is no ||, $?, here-document or backquote. A script stops at its first error, and the error is the result. A script cannot reach the FIFOs of a home. Each call is one Request to mkfifo.com, with its limits: 1 MiB of output, and the work of one Request.","inputSchema":{"type":"object","properties":{"script":{"type":"string","description":"The script, one command or more, one on each line."}},"required":["script"],"additionalProperties":false},"annotations":{"readOnlyHint":false,"destructiveHint":false,"openWorldHint":true}}],"ttlMs":3600000,"cacheScope":"public"})}')

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server/discover: the versions of MCP that this endpoint speaks, its capabilities and its instructions.

Egress envelopes of ingress envelope 5

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-702b-84e3-fd2fdbf486ab@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, result: ({resultType: "complete", _meta: {"io.modelcontextprotocol/serverInfo":{"name":"mkfifo.com","title":"mkfifo.com","version":"1"}}} + {"supportedVersions":["2026-07-28","2025-11-25","2025-06-18","2025-03-26"],"capabilities":{"tools":{"listChanged":false}},"instructions":"mkfifo.com is a named pipe for the web. A FIFO is a name, for example https://mkfifo.com/my-shop or my-shop@mkfifo.com, and its envelopes are its rules: they take its Requests (HTTP and email) and send them on. The tool run runs a script of the FIFO shell, the shell of https://mkfifo.com//bin/sh and of the terminal of the editor. A Request to a FIFO is a pipe or a redirection in the script. Each person who knows the name of a public FIFO can read and change its envelopes, so use a long random name for your own work. Docs: https://mkfifo.com/docs","ttlMs":3600000,"cacheScope":"public"})}')

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initialize, the first request of a client of an older version. The answer has the version of the client when this endpoint speaks it, else 2025-11-25.

Egress envelopes of ingress envelope 6

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7033-95c3-2ef105f8b357@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c --arg version "$version" '{jsonrpc: "2.0", id: .id, result: {protocolVersion: (if ($version | IN("2025-11-25", "2025-06-18", "2025-03-26")) then $version else "2025-11-25" end), capabilities: {tools: {listChanged: false}}, serverInfo: {"name":"mkfifo.com","title":"mkfifo.com","version":"1"}, instructions: "mkfifo.com is a named pipe for the web. A FIFO is a name, for example https://mkfifo.com/my-shop or my-shop@mkfifo.com, and its envelopes are its rules: they take its Requests (HTTP and email) and send them on. The tool run runs a script of the FIFO shell, the shell of https://mkfifo.com//bin/sh and of the terminal of the editor. A Request to a FIFO is a pipe or a redirection in the script. Each person who knows the name of a public FIFO can read and change its envelopes, so use a long random name for your own work. Docs: https://mkfifo.com/docs"}}')

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ping: an empty result.

Egress envelopes of ingress envelope 7

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-703b-b263-f7096e8274fe@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, result: ({resultType: "complete", _meta: {"io.modelcontextprotocol/serverInfo":{"name":"mkfifo.com","title":"mkfifo.com","version":"1"}}} + {})}')

Show the body Show the header

ping, for a client of an older version.

Egress envelopes of ingress envelope 8

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7043-9995-0f524349306c@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, result: ({resultType: "complete", _meta: {"io.modelcontextprotocol/serverInfo":{"name":"mkfifo.com","title":"mkfifo.com","version":"1"}}} + {})}')

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tools/call for a tool that is not run: the error -32602.

Egress envelopes of ingress envelope 9

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-704b-9a3a-901763b40261@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32602, message: ("Unknown tool: " + (.params.name | tostring))}}')

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A tool that is not run, for a client of an older version: the error -32602.

Egress envelopes of ingress envelope 10

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7053-8285-b7dcbb21263b@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32602, message: ("Unknown tool: " + (.params.name | tostring))}}')

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A method that this endpoint does not have: 404, with the error -32601.

Egress envelopes of ingress envelope 11

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-705b-95a5-fcc43887f278@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32601, message: ("Method not found: " + .method)}}')

Show the body Show the header

A method that this endpoint does not have, for a client of an older version: the error -32601.

Egress envelopes of ingress envelope 12

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7063-b471-04c38c521cd5@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32601, message: ("Method not found: " + .method)}}')

Show the body Show the header

A notification, a message with no id, such as notifications/initialized: 202, with no body.

Egress envelopes of ingress envelope 13

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-706b-9825-b19882fae6e5@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

Show the body Show the header

A request from a page of a different site: 403. So a different site cannot use this tool from the browser of its visitor.

Egress envelopes of ingress envelope 14

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7073-ab38-d5020a2f15ef@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

{"jsonrpc":"2.0","error":{"code":-32600,"message":"This request comes from a different site: the Origin is not mkfifo.com."}}

Show the body Show the header

A GET that asks for a stream of events: 405. This endpoint has no stream: each answer is one JSON message.

Egress envelopes of ingress envelope 15

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-707b-9b76-7f509dea9bca@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

{"jsonrpc":"2.0","error":{"code":-32600,"message":"This MCP endpoint takes only POST, with one JSON-RPC message."}}

Show the body Show the header

A body that is not JSON: the error -32700.

Egress envelopes of ingress envelope 16

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7083-9014-133e2adec5e5@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

{"jsonrpc":"2.0","error":{"code":-32700,"message":"Parse error: the body is not JSON."}}

Show the body Show the header

JSON that is not one JSON-RPC 2.0 message, such as a batch: the error -32600.

Egress envelopes of ingress envelope 17

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-708b-b3d0-f6d744aec97d@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

{"jsonrpc":"2.0","error":{"code":-32600,"message":"Invalid request: the body is not one JSON-RPC 2.0 message."}}

Show the body Show the header

A message with no method: the error -32600.

Egress envelopes of ingress envelope 18

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-7093-947d-f70eddaeeba0@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32600, message: "Invalid request: the message has no method."}}')

Show the body Show the header

A request whose id is null: the error -32600.

Egress envelopes of ingress envelope 19

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-709b-8cd0-899cccb1ccad@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

{"jsonrpc":"2.0","error":{"code":-32600,"message":"Invalid request: the id of a request must not be null."}}

Show the body Show the header

A version of MCP that this endpoint does not speak: the error -32022, with the versions that it speaks.

Egress envelopes of ingress envelope 20

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70a3-bcf8-72fde9826dd1@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c --arg version "$version" '{jsonrpc: "2.0", id: .id, error: {code: -32022, message: "Unsupported protocol version", data: {supported: ["2026-07-28","2025-11-25","2025-06-18","2025-03-26"], requested: $version}}}')

Show the body Show the header

The header MCP-Protocol-Version and the version in _meta are different: the error -32020.

Egress envelopes of ingress envelope 21

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70ab-92da-7e83c4f38d06@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32020, message: "Header mismatch: the MCP-Protocol-Version header does not match io.modelcontextprotocol/protocolVersion in _meta."}}')

Show the body Show the header

A request of version 2026-07-28 with no version in _meta: the error -32602.

Egress envelopes of ingress envelope 22

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70b3-96e2-bfea0c3e3126@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32602, message: "Invalid params: _meta has no io.modelcontextprotocol/protocolVersion."}}')

Show the body Show the header

A request of version 2026-07-28 with no client capabilities in _meta: the error -32602.

Egress envelopes of ingress envelope 23

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70bb-aaf9-c5cde4f14066@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32602, message: "Invalid params: _meta has no io.modelcontextprotocol/clientCapabilities."}}')

Show the body Show the header

A version in _meta, but no header MCP-Protocol-Version for it: the error -32020.

Egress envelopes of ingress envelope 24

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70c3-9e12-a041d1de7597@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32020, message: "Header mismatch: the MCP-Protocol-Version header is missing, or does not match io.modelcontextprotocol/protocolVersion in _meta."}}')

Show the body Show the header

The header Mcp-Method and the method in the body are different: the error -32020.

Egress envelopes of ingress envelope 25

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70cb-b80e-c10fecbf4ca4@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32020, message: "Header mismatch: the Mcp-Method header does not match the method of the body."}}')

Show the body Show the header

The header Mcp-Name names run, but the body names a different tool: the error -32020.

Egress envelopes of ingress envelope 26

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70d3-ae64-ce3dad47a346@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32020, message: "Header mismatch: the Mcp-Name header does not match the name of the tool in the body."}}')

Show the body Show the header

The body names run, but the header Mcp-Name is missing or names a different tool: the error -32020.

Egress envelopes of ingress envelope 27

Egress envelope 1

In reply to an ingress envelope of this FIFO

To:

Other header fields of Egress envelope 1
Seal: mkfifo.com encrypts the value when you save, and never shows it again.

Message-ID <01a14722-b29d-70db-b81c-c2fc4af93a80@mkfifo.com>

Body of egress envelope 1
The text of the message. $name inserts a capture from the ingress envelope.

$($rpc | jq -c '{jsonrpc: "2.0", id: .id, error: {code: -32020, message: "Header mismatch: the Mcp-Name header does not match the name of the tool in the body."}}')

Show the body Show the header