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mitmweb-mcp

One UI. You watch it, your AI reads it.

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An MCP server that reads the mitmweb session you are already running — the same flows, the same window, the same moment.

You keep the mitmweb UI open and drive the browser yourself. Your AI assistant sees exactly what you see, and can search it, diff it, replay it, and turn it into a runnable scraper.

                     ┌──────────────► browser UI      (you)
  browser ──proxy──► mitmweb (:8080 proxy / :8081 API+UI)
                     └──────────────► mitmweb-mcp ───► AI assistant
                          one process · one flow list

Why this exists

Other mitmproxy MCP servers spin up their own headless proxy. That gives you two separate capture sessions: the one you are looking at, and the one the AI is looking at. To reconcile them you have to either chain the two proxies (longer path, two TLS hops, doubled latency) or accept that the two views disagree.

mitmweb-mcp takes a different route. The insight is that mitmweb's own frontend is just an HTTP client — the flow list you see in the browser comes from GET /flows.json, and clicking into a body calls GET /flows/<id>/response/content.data. That REST API has always been there; nobody treats it as an API.

So this server starts no proxy at all. It is a second, parallel client of the mitmweb you already have. Three properties fall directly out of that architecture, with no synchronisation machinery needed:

  1. What the UI shows is what the AI reads. One process, one in-memory flow list.

  2. Zero added latency. Nothing is inserted into the request path. Your browsing feels exactly as it did before.

  3. If the MCP server dies, capture keeps running. It is only a reader.

Related MCP server: playwriter

Safety model: read-only and append-only

Nine of the ten tools are plain GET requests and cannot alter your session. replay_flow does not modify existing flows either — it re-sends a request, which appends a new flow. The worst case is a few extra rows; nothing you are looking at can silently change or disappear.

There is deliberately no clear_flows tool. Wiping the session is destructive and irreversible, it is one click in the UI, and there is no reason to hand an AI that button.


Install

Requires Python ≥ 3.10 and mitmproxy ≥ 10 on your PATH.

pip install mitmweb-mcp

Or from source:

git clone https://github.com/numb747/mitmweb-mcp
cd mitmweb-mcp
pip install -e .

Setup

1. Start mitmweb with a fixed token

mitmweb generates a random web password at every launch, which this server has no way to discover. Pin it:

mitmweb --listen-port 8080 --set web_password=YOUR_SECRET_TOKEN
  • 8080 is the proxy port — point your browser here (replays go through it too)

  • 8081 is the UI + API — you watch this, and so does the MCP server

Trust mitmproxy's CA once so HTTPS works: browse to http://mitm.it through the proxy, or import ~/.mitmproxy/mitmproxy-ca-cert.pem.

Optionally start with a cleaner view: --set view_filter='!~a & !~d googleapis.com'

2. Register the MCP server

Claude Code:

claude mcp add mitmweb -s user \
  -e MITMWEB_URL=http://127.0.0.1:8081 \
  -e MITMWEB_TOKEN=YOUR_SECRET_TOKEN \
  -e MITMPROXY_PORT=8080 \
  -- mitmweb-mcp

Claude Desktop (claude_desktop_config.json) or any MCP client:

{
  "mcpServers": {
    "mitmweb": {
      "command": "mitmweb-mcp",
      "env": {
        "MITMWEB_URL": "http://127.0.0.1:8081",
        "MITMWEB_TOKEN": "YOUR_SECRET_TOKEN",
        "MITMPROXY_PORT": "8080"
      }
    }
  }
}

Variable

Default

Must match

MITMWEB_URL

http://127.0.0.1:8081

mitmweb's web_port

MITMWEB_TOKEN

(empty)

mitmweb's web_password

MITMPROXY_PORT

8080

mitmweb's --listen-port

Restart your MCP client, then ask it to run status to confirm the connection.


Tools

Tool

What it does

status

Connectivity check and flow count. Start here when debugging.

flow_stats

Hosts, status codes, asset ratio, hottest endpoints (numeric ids normalised to {n}).

list_flows

Recent flows, newest first. Filter by host, method, status, URL, content-type, time window, or UI mark.

inspect_flow

One flow in full: query params, both header sets, both bodies, latency, and a ready-to-run curl.

get_content

A complete body, gzip/brotli already decoded.

search_flows

Full-text search across all flows, optionally regex.

diff_flows

Compare two requests field by field.

detect_auth

Identify which auth schemes the site uses and where the credentials live.

generate_code

Emit a runnable scraper: curl_cffi, httpx, requests, or a shell script.

replay_flow

Re-send a request with browser TLS fingerprinting; optionally rewrite method, headers, or body.

Flow ids can be the 8-character short form that list_flows returns — they are matched by prefix.

Three design details worth knowing

Static assets are excluded by default. A modern page produces hundreds of flows of which maybe five matter. list_flows applies the equivalent of mitmproxy's !~a filter unless you pass include_assets=True. Binary bodies are never decoded into mojibake; you get <binary image/png, 8090 bytes, omitted> instead.

Your UI actions are usable as input. This is the payoff of sharing one session, and no headless design can offer it:

  • list_flows(marked_only=True) — mark a few flows in the mitmweb UI, and the AI analyses only those.

  • list_flows(since_seconds=15) — you just clicked a button; this isolates exactly what that click triggered.

Replay goes through your proxy. mitmweb's native replay endpoint is protected by Tornado's XSRF, whose cookie is only issued to the /updates websocket. Rather than maintain a websocket for that, replay_flow re-sends the request through your own proxy — so the result lands in your UI anyway, and you gain capabilities the native replay does not have: TLS/JA3 fingerprint impersonation via curl_cffi, arbitrary header and body rewriting, and allow_redirects=False so every hop stays visible.


A worked example

1 — Find the endpoint behind something you can see

"The order number SO20260910 is on this page. Which request returned it?"

search_flows("SO20260910")   → POST /api/order/list
inspect_flow("a3f21b8c")     → signing headers, body shape, equivalent curl

2 — Work out which parameters are signed

Trigger the same action twice, then:

diff_flows("a3f21b8c", "c44a48f7")
{
  "same_endpoint": true,
  "query_diff": { "changed": { "nonce": { "a": "aaa", "b": "bbb" } } },
  "body_diff":  { "changed": { "sign":    { "a": "1111", "b": "2222" },
                               "meta.ts": { "a": 1000,   "b": 2000   } } }
}

Identical fields are omitted, so what remains is the answer: the signature covers a nonce and a timestamp. page and meta.ver never varied, so they are not part of it.

3 — Confirm it reproduces outside the browser

replay_flow("a3f21b8c")                     → same 200, no browser involved
replay_flow("a3f21b8c", body={"page": 2})   → probe paging and edge cases

Every replay appears in your UI as you go.

4 — Ship it

generate_code(["a3f21b8c"], framework="curl_cffi")
#!/usr/bin/env python3
"""Generated by mitmweb-mcp from captured traffic.

Adapt as needed: add paging loops, concurrency, retries, error handling."""
from curl_cffi.requests import Session

IMPERSONATE = 'chrome'


def main() -> None:
    with Session(impersonate=IMPERSONATE) as s:

        # --- 1. POST /api/order/list (originally returned 200) ---
        r1 = s.post(
            'https://example.com/api/order/list',
            params={'page': '1'},
            headers={'Authorization': 'Bearer ...', 'Content-Type': 'application/json'},
            json={'page': 1, 'sign': '1111'},
        )
        print("1.", r1.status_code, r1.text[:200])


if __name__ == "__main__":
    main()

Pass several ids to generate a multi-step script — the requests share one Session, so a "log in, then call the API" sequence carries its cookies across.


Scope

This server is the analysis layer. Capture, live interception with breakpoints, and clearing the session stay in the mitmweb UI, where they belong — interception in particular is inherently interactive and there is nothing to gain from proxying it through an AI.

For unattended bulk capture, use mitmdump with an addon script; that is a different job from the one this tool does.


Development

git clone https://github.com/numb747/mitmweb-mcp
cd mitmweb-mcp
python -m venv .venv && source .venv/bin/activate
pip install -e ".[dev]"

ruff check .
python tests/test_e2e.py     # needs mitmproxy on PATH and internet access

The end-to-end test launches a real mitmweb on ports 18080/18081, pushes traffic with known marker values through it (including the same endpoint called twice with only nonce/sign/ts differing, to exercise diff_flows), then drives every tool over a real MCP stdio session. It asserts 56 behaviours, including that generated code compiles and that diff_flows omits fields which did not change.

Two things that will bite you

GET /flows/<id> returns 405. /flows.json is the only list endpoint and it returns everything, at roughly 2.6 KB per flow. The 2-second TTL cache is therefore a correctness-of-cost requirement, not a micro-optimisation. Similarly, search_flows fetches bodies concurrently — serially it would be hundreds of round-trips.

FastMCP pre-parses JSON string arguments. A parameter annotated str that receives a valid JSON string gets parsed into a dict before validation, which then fails with Input should be a valid string. This is why replay_flow annotates headers and body as dict | str | None.

Contributing

Issues and pull requests are welcome. Please run ruff check . and the end-to-end test before opening a PR.

License

MIT — see LICENSE.

Acknowledgements

Built on mitmproxy and curl_cffi.

Available Tools

10 tools
detect_authA

Scan all traffic and report which authentication schemes the site uses.

Run this when picking up an unfamiliar target: it answers "what exactly do I have to forge in order to call this API without a browser?" — a bearer token, a session cookie, a custom API-key header, or a signed request. Each finding includes sample flow ids you can pass straight to inspect_flow.

ParametersJSON Schema
NameRequiredDescriptionDefault

No parameters

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.5/5.0
Behavior4/5

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

With no annotations, the description carries the burden of explaining behavior. It discloses that the tool scans all traffic, reports auth schemes, and that findings include sample flow ids. This goes beyond the empty input schema and gives useful implementation detail about the result format.

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 compact and front-loaded with the core purpose, followed by the when-to-use guidance and a practical pointer to a sibling tool. Every sentence adds value and there is no redundant restating of the tool name.

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

Completeness5/5

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

For a zero-parameter tool with an output schema, the description is complete: it explains when to run it, what it reports, and how to use the results downstream. The reference to inspect_flow contextualizes the output within the sibling toolset.

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

Parameters4/5

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

The input schema has zero parameters, so the baseline is 4. The description adds context about what the tool does with no arguments and what kind of output to expect, which is sufficient for an agent to invoke it correctly.

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 states a specific verb ('scan and report') and a clear resource ('which authentication schemes the site uses'). It is immediately distinguishable from sibling tools like inspect_flow or list_flows because it addresses the high-level question of what credentials/mechanisms are needed.

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?

It gives an explicit trigger: 'Run this when picking up an unfamiliar target.' It also names a specific follow-up tool (inspect_flow) and explains how the output feeds into it. It does not explicitly list when not to use it, but the intended context is clear.

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

diff_flowsA

Compare two requests field by field — the tool for reverse-engineering signatures.

Typical use: call the same endpoint twice (or capture it before and after paging), then diff. Parameters that stay the same are omitted from the output, so what remains is exactly the set that varies per request: nonce, timestamp, signature. That tells you which fields any signing algorithm must reproduce.

JSON bodies are flattened to a.b.c keys and compared per key. Non-JSON bodies are returned verbatim for both sides so you can judge them yourself.

ParametersJSON Schema
NameRequiredDescriptionDefault
body_maxNo
flow_id_aYes
flow_id_bYes

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.1/5.0
Behavior4/5

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

With no annotations, the description carries the full burden and discloses rich behavior: unchanged parameters are omitted from output, JSON bodies are flattened to a.b.c keys and compared per key, and non-JSON bodies are returned verbatim. The only gap is that the effect of body_max is never disclosed.

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?

Three dense paragraphs, each earning its place: purpose, usage workflow, and body-handling semantics. The core purpose is front-loaded and the explanatory detail about output omission and flattening is tightly written with no filler.

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

Completeness4/5

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

An output schema exists, so return values need no explanation. The description covers purpose, workflow, output semantics, and JSON/non-JSON handling comprehensively. The remaining gaps are the unexplained body_max parameter and whether headers are compared alongside bodies.

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?

With 0% schema description coverage, the description must compensate. It contextualizes the two required flow_id parameters well ('call the same endpoint twice'), but never explicitly maps them to the schema fields and leaves body_max entirely unexplained despite it having a default value.

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 opening line 'Compare two requests field by field — the tool for reverse-engineering signatures' states a specific verb, resource, and a distinctive purpose that separates it from siblings like inspect_flow (single flow) and replay_flow (execution). An agent can tell exactly what this tool is for without opening the schema.

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?

Gives clear when-to-use context: 'call the same endpoint twice (or capture it before and after paging), then diff.' It explains what the output means and how to interpret the varying fields for signature reverse-engineering. However, it does not explicitly name sibling alternatives or state when not to use it.

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

flow_statsA

Overview of captured traffic: hosts, status codes, asset ratio, hottest endpoints.

This is the first thing to run against an unfamiliar site: it tells you which host the interesting API lives on and whether anything is failing. Numeric path segments are normalised to {n}, so /user/1001 and /user/1002 are counted as one endpoint.

ParametersJSON Schema
NameRequiredDescriptionDefault
top_endpointsNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A3.9/5.0
Behavior3/5

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

No annotations are provided, so the description must carry the burden. It does disclose one important behavioral trait: 'numeric path segments are normalised to {n}', which is a non-obvious aggregation behavior. However, it doesn't explicitly state whether the tool is read-only, whether any caching/rate limits apply, or any other side effect. The normalization detail earns a 3.

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?

Three sentences each earn their place: the first is a dense summary of what the tool returns, the second gives context and value, the third explains a critical data-normalization rule. Zero padding, front-loaded with the resource and purpose.

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

Completeness4/5

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

Given the tool's low complexity (one optional param, an output schema exists, and no nested objects), the description is largely complete. It explains what it reports, when to use it, and one important normalization behavior. It doesn't elaborate on the parameter or detail 'asset ratio', but the output schema covers return details. A 4 is appropriate.

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

Parameters2/5

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

The description does not mention the sole parameter 'top_endpoints' at all. Schema description coverage is 0%, so the description should compensate, but it only says 'hottest endpoints', leaving the relationship between the parameter and the result implied. The parameter's name is a slight hint but the description adds essentially no semantic value beyond that.

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 opens with a clear verb and resource: 'Overview of captured traffic' and then specifies the exact dimensions (hosts, status codes, asset ratio, hottest endpoints). It also contains a strong distinguisher from siblings: 'the first thing to run against an unfamiliar site' is positioning that separates it from inspect_flow, search_flows, and replay_flow.

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?

Explicit usage context is given: 'This is the first thing to run against an unfamiliar site' and it explains why it helps (tells you the interesting host and whether anything is failing). It doesn't name specific sibling tools for non-existent cases, so it's clear but lacks exclusions, putting it at a 4.

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

generate_codeA

Turn captured flows into a runnable scraper script — the final deliverable.

flow_ids may be a list or a comma-separated string. The order is preserved in the generated script and all requests share one Session, so a "log in, then call the API" sequence replays correctly with cookies carried across.

framework = curl_cffi (default; TLS fingerprint impersonation, best for scraping) | httpx | requests | curl (emits a shell script instead).

Original request headers are kept, minus the ones the client manages itself.

ParametersJSON Schema
NameRequiredDescriptionDefault
body_maxNo
flow_idsYes
frameworkNocurl_cffi
impersonateNochrome

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.1/5.0
Behavior4/5

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

No annotations are provided, so the description carries the full burden, and it discloses several important behaviors: order is preserved, requests share one Session for cookie continuity, and specific framework defaults are explained. It also mentions that original headers are kept except client-managed ones. It does not cover all nuances like body_max or impersonate behavior, but the disclosed behavior is substantive.

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 efficient and front-loaded, with the first sentence stating the purpose immediately. Each subsequent sentence adds useful information about input formats, frameworks, or headers. It's not perfectly tight—the header and framework details could be merged without loss—but it earns a solid 4.

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

Completeness4/5

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

Given the complexity of 4 parameters and 0% schema coverage, the description covers the key usage behaviors well: input formats, ordering, session/cookie continuity, framework variations, and header filtering. It lacks explanation for body_max, impersonate, and the precise nature of the return value, but the presence of an output schema mitigates the last missing piece.

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 0%, requiring the description to compensate, and it does for flow_ids by clarifying that it accepts a list or comma-separated string with order preservation. It also explains the framework parameter meaningfully (curl_cffi default, curl emits a shell script). However, body_max and impersonate and both left unexplained, adding deficient coverage for 2 of 4 parameters.

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 a specific verb and resource: 'Turn captured flows into a runnable scraper script'. It also states its role as 'the final deliverable', which distinguishes it from siblings like replay_flow or inspect_flow. An agent can tell this tool produces code rather than executing or analyzing flows.

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 provides clear context by framing the tool as the end deliverable producer, suggesting use at the finalization stage. However, it does not explicitly point to alternatives or state when not to use it (e.g., 'use replay_flow to test instead'). It earns a 4 for clear context without exclusions.

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

get_contentA

Fetch one full body (gzip/brotli already decoded). which = request | response.

Use this instead of inspect_flow when the body is large and you need more than inspect_flow's 4000-character preview.

ParametersJSON Schema
NameRequiredDescriptionDefault
whichNoresponse
flow_idYes
max_bytesNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.1/5.0
Behavior3/5

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

With no annotations, the description carries the burden. It states the body is already decoded (gzip/brotli), which is useful behavioral context. However, it does not disclose potential performance impacts, rate limits, or what happens when max_bytes is exceeded. The decoding note adds value, but it's minimal.

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 concise, with two sentences: the first states the core purpose, and the second provides usage guidance. It is front-loaded with the most important information and contains no fluff.

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

Completeness4/5

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

The tool is simple, but the description omits details like what happens when max_bytes is exceeded, whether partial bodies are returned, or error handling. Since an output schema exists, return format is covered elsewhere, but behavioral nuances are missing. Still, for a straightforward fetch tool, it is adequate.

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

Parameters2/5

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

Schema description coverage is 0%, so the description must compensate. The description mentions 'which = request | response' and implies max_bytes for large bodies, but doesn't explain the meaning of flow_id or the default behavior of max_bytes. It does not fully specify parameter formats or constraints, leaving gaps.

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 tool's purpose: fetching the full body of a request or response, with gzip/brotli already decoded. It distinguishes itself from sibling tool inspect_flow by specifying it is for large bodies, contrasting with inspect_flow's 4000-character preview.

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

Usage Guidelines5/5

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

The description explicitly says 'Use this instead of inspect_flow when the body is large and you need more than inspect_flow's 4000-character preview.' This provides clear when-to-use guidance and names the alternative, fulfilling the dimension perfectly.

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

inspect_flowA

Full detail for one flow: URL, query params, both header sets, both bodies, latency, and a ready-to-run equivalent curl command.

ParametersJSON Schema
NameRequiredDescriptionDefault
flow_idYes
body_maxNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A3.6/5.0
Behavior3/5

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

With no annotations, the description carries the burden of explaining behavior. It usefully details what the tool returns e.g., both header sets, both bodies, latency, curl command, but it does not explicitly state that this is a read-only operation or disclose constraints like body_max truncation or potential errors.

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 tightly written sentence that front-loads the core purpose and then packs concrete useful specifics. Every listed item earns its place, and there is no fluff or repetition.

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?

An output schema exists, so return values need not be explained. However, the description omits any guidance on body_max and does not explicitly route the agent toward this tool versus siblings Morgue. It is adequate for a simple inspect operation but has clear gaps around parameter behavior and when to use it.

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

Parameters2/5

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

Schema description coverage is 0%, so the description must compensate. It implies flow_id selects the flow to inspect, but body_max is completely unexplained and its relationship to 'both bodies' is unclear. The agent cannot infer the significance of body_max from the description.

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 opens with a specific verb and resource: 'Full detail for one flow.' It then enumerates the exact contents returned (URL, query params, headers, bodies, latency, curl command), making it easy to distinguish from siblings like list_flows, flow_stats, or diff_flows.

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?

The phrase 'Full detail for one flow' implies this is for deep inspection of a single flow rather than listing or comparing, but it never explicitly states when to choose this over siblings or provides any exclusion criteria. The usage context is clear but only implied.

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

list_flowsA

List recent flows, newest first.

Static assets (js/css/images/fonts) are excluded by default — the equivalent of mitmproxy's !~a filter, and the single biggest signal-to-noise win. Pass include_assets=True when you actually want them.

Two parameters make the human's UI actions usable as input:

  • since_seconds: only flows from the last N seconds. If the user just clicked a button, since_seconds=15 isolates exactly what that click triggered.

  • marked_only: only flows the user has marked in the mitmweb UI.

url_contains matches the full URL including host and query string; content_type is a substring match against the response type, e.g. "json".

ParametersJSON Schema
NameRequiredDescriptionDefault
hostNo
limitNo
methodNo
marked_onlyNo
status_codeNo
content_typeNo
url_containsNo
since_secondsNo
include_assetsNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4/5.0
Behavior4/5

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

With no annotations, the description carries the burden and discloses meaningful behavior: newest-first ordering, default asset exclusion with the include_assets escape hatch, and exact matching semantics for url_contains and content_type. It stops short of mentioning pagination, rate limits, or auth, but the output schema likely covers return shape.

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 front-loaded with the purpose and then organized by behavior and parameter guidance; most sentences earn their place. The 'single biggest signal-to-noise win' phrase is slightly promotional but harmless, and the paragraph breaks make it scannable.

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

Completeness4/5

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

For a 9-parameter tool with no annotations, the description covers the core list filtering behavior, asset exclusion, and matching details. It does not explicitly route to search_flows for more complex search scenarios, and a few parameters are undocumented, but the output schema and obvious parameter names fill most remaining gaps.

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

Parameters4/5

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

The description adds non-obvious semantics for include_assets, since_seconds, marked_only, url_contains, and content_type beyond the bare schema, which has 0% description coverage. Host, limit, method, and status_code are left to their self-explanatory names/defaults, which is a minor gap but not a fatal one.

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?

Purpose is immediately stated as 'List recent flows, newest first' — a specific verb, resource, and ordering. It is clearly distinct from inspect_flow, get_content, or diff_flows, though it does not explicitly call out search_flows as the alternative for more complex queries.

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 gives concrete usage context: static assets are excluded by default unless include_assets=True, since_seconds is framed as isolating a user's UI click, and marked_only targets flows marked in the UI. It does not state when to prefer list_flows over search_flows, so no explicit exclusion or alternative is given.

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

replay_flowA

Replay a request, optionally rewriting method, headers or body (like Burp Repeater).

The request is sent with curl_cffi using browser TLS fingerprint impersonation, and it goes through your own mitmproxy, so the result appears as a new flow in your mitmweb UI where you can see it. Existing flows are never modified.

headers overrides or adds headers, e.g. {"Authorization": "Bearer NEW"}; omit to reuse the original. body replaces the request body (dicts/lists are serialised to JSON). impersonate accepts chrome / chrome131 / chrome142 / safari / firefox / edge.

ParametersJSON Schema
NameRequiredDescriptionDefault
bodyNo
methodNo
flow_idYes
headersNo
timeoutNo
body_maxNo
impersonateNochrome

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.4/5.0
Behavior4/5

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

With no annotations, the description carries the full burden, and it does well: it discloses that the request goes through mitmproxy with curl_cffi/browser impersonation, that this creates a new flow in mitmweb, and that existing flows are never modified. It could add what happens on timeout or failure, but the key behavioral safety profile is clear.

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?

Three short paragraphs each earn their place: purpose, side-effect/behavior, and parameter semantics. The most important scoping statement ('existing flows are never modified') is placed early, and the example makes the headers semantics concrete without bloat.

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

Completeness4/5

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

The description covers what the tool does, how the request is transported, the side effect in the UI, and how the main optional parameters behave. Given that an output schema exists, return values are not required; minor gaps around body_max/timeout keep this from a 5.

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

Parameters4/5

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

Despite 0% schema description coverage, the description explains the important parameters: header override/add semantics with an example, body replacement with JSON serialization for dicts/lists, and accepted impersonate values. It leaves timeout and body_max to their names/defaults, but the core parameters are meaningfully documented.

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?

States the precise action 'Replay a request' and immediately adds the optional modifications (method, headers, body), so an agent knows exactly what the tool does. The 'like Burp Repeater' analogy and the note that it creates a new flow while existing flows are never modified clearly separate it from the inspection/status/diff sibling tools.

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 gives clear context: it is for replaying a captured request, optionally rewriting it, and observing the result as a new flow in mitmweb. It does not explicitly compare itself to sibling tools like inspect_flow or generate_code, so it stops short of a 5.

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

search_flowsA

Full-text search across flows: "which request carried or returned this value?"

This is the usual entry point for reverse-engineering an API. Take a distinctive value visible in the page (an order number, a username, a token) and search for it to find the endpoint that produced it.

scope = all | url | headers | body. With regex=True the keyword is a regular expression, e.g. "sign=[a-f0-9]{32}". Scans backwards from the newest flow, at most max_scan flows.

ParametersJSON Schema
NameRequiredDescriptionDefault
limitNo
regexNo
scopeNoall
keywordYes
max_scanNo
include_assetsNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.2/5.0
Behavior4/5

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

With no annotations provided, the description carries the full disclosure burden. It does well by explaining search scope values, regex behavior, backward scanning order, and the max_scan bound. It does not clarify how limit or include_assets affect results, which is a real but minor transparency gap.

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 efficiently structured in three short sections: core purpose, motivating use case, and technical parameter details. It is front-loaded with the most important information and contains no filler or repetition.

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

Completeness4/5

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

For a search tool with an output schema, the description covers the core invocation path thoroughly: what to search, why, how scope works, and scan limits. The main omissions are the semantics of limit and include_assets, and the lack of explicit guidance on when not to use this tool versus siblings.

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 0%, so the description must compensate. It adds real meaning for keyword, scope, regex, and max_scan, including a concrete regex example. However, it completely omits limit and include_assets, leaving two of six parameters semantically undefined.

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 opens with a specific verb and resource: 'Full-text search across flows'. It also articulates the exact question the tool answers ('which request carried or returned this value?') and frames it as the entry point for reverse-engineering an API, making it easy to distinguish from sibling tools like list_flows or inspect_flow.

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?

Usage guidance is explicit and actionable: it says this is the usual entry point for reverse-engineering an API and gives a concrete workflow (take a distinctive value visible in the page, search for it, find the endpoint). It does not explicitly name alternatives or exclusion criteria, but the use case is clear enough to route an agent.

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

statusA

Check connectivity to mitmweb and report how many flows are captured.

Start here when something is not working.

ParametersJSON Schema
NameRequiredDescriptionDefault

No parameters

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.1/5.0
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 state whether the operation is read-only, has side effects, requires authentication, or has any latency considerations. Although the purpose implies a simple connectivity check, the absence of any explicit behavioral disclosure is a notable gap.

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 two short sentences with zero fluff. The primary action ('Check connectivity... and report how many flows are captured') is front-loaded, immediately followed by usage guidance ('Start here when something is not working'). Every word earns its place.

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

Completeness5/5

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

Given the tool's simplicity (no parameters, an output schema is present), the description sufficiently covers the purpose and usage. The existence of an output schema means return values are documented separately, so the description need not explain them. The tool is a simple status check, and the description provides all necessary context for an agent to call it correctly.

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

Parameters4/5

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

The tool has zero parameters, so the description need not explain parameter behavior. The schema coverage is 100% (no properties), and the baseline for zero parameters is 4. The description adds no parameter info because none exist, which 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: 'Check connectivity to mitmweb' and the outcome: 'report how many flows are captured.' This specific verb+resource pairing distinguishes it from sibling tools like list_flows (which lists flows) and flow_stats (which likely gives detailed statistics). The phrase 'Start here when something is not working' adds a clear diagnostic role, cementing its unique purpose.

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 provides explicit when-to-use guidance: 'Start here when something is not working.' This implies it is the first diagnostic step when connectivity or flow capture is suspected to be failing. However, it does not explicitly list alternatives or state when not to use it, so it stops short of the full 5.

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

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

  1. 10 tool updatesv0.1.0
    • First observeddetect_auth
    • First observeddiff_flows
    • First observedflow_stats
    • First observedgenerate_code
    • First observedget_content
    • First observedinspect_flow
    • First observedlist_flows
    • First observedreplay_flow
    • First observedsearch_flows
    • First observedstatus

TDQS

A4.2/5.0

Scored across 10 tools

Disambiguation5/5

Every tool has a clearly distinct purpose: status checks connectivity, flow_stats provides an overview, inspect_flow gives full detail, detect_auth scans authentication, list_flows lists flows, get_content fetches full bodies, search_flows performs full-text search, diff_flows compares requests, generate_code produces scripts, and replay_flow replays requests. No two tools overlap in intent; even get_content and inspect_flow differ in scope (full vs. preview).

Naming Consistency5/5

All tool names follow a consistent lowercase_snake_case convention with a verb-first pattern (inspect_flow, detect_auth, list_flows, get_content, search_flows, diff_flows, generate_code, replay_flow) and a few exceptions like status and flow_stats that still fit the overall style. No mixing of camelCase or different naming schemes.

Tool Count5/5

With 10 tools, the set is well-scoped for a traffic capture and analysis server. Each tool covers a distinct aspect of the workflow: connectivity, overview, inspection, auth detection, listing, body retrieval, search, diffing, code generation, and replay. The count feels neither thin nor bloated.

Completeness5/5

The tool surface covers the full lifecycle of working with captured HTTP traffic: connect, summarize, inspect, search, compare, generate code, and replay. It also includes advanced features like auth detection and body extraction. There are no obvious dead ends—each tool feeds into the next, and the domain is thoroughly addressed.

Maintenance

ActivityMaintained
ResponsivenessNo issues

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