The request inspector

Follow a request all the way through.

Scan compact, numbered rows without losing your place. Select a request to see its status, timing and response content; open the full viewer for headers and the complete exchange.

Explore the interactive demo →

ProxyCat desktop inspecting a numbered POST request with a 201 status, timing and JSON response — Request summary and response bodyDesktop preview · sample traffic

Compose & repeat

Change the input. See what happens.

Open a captured request as an editable draft. Change its URL, headers or body, then send it and inspect the response beside your input. Repeat the original when you need the same request bytes again.

Each send goes directly to the destination with TLS validation and creates a new numbered capture within your plan’s allowance. Proxy rewrite and throttle rules do not apply to these direct sends.

Try the guided examples →

ProxyCat desktop composer showing an editable POST request, JSON headers and body, and a formatted 201 response alongside it — Edit, send and inspect side by sideDesktop preview · sample traffic

Compare captures

Find what changed between failure and success.

Keep a request as your baseline, select the next attempt, and compare them side by side. See the method, URL, status, timing, headers and body differences without juggling two inspector windows.

Focus on changes only, or format JSON to remove formatting noise. Binary payloads show byte counts and hashes; incomplete captures are labelled, so a missing body never looks like a match.

Explore the sample traffic →

Native ProxyCat comparison of a failed order response and a successful retry, with aligned JSON differences — From a quantity error to a created orderDesktop preview · sample traffic

Network controls

Test the slow connection before your users do.

Choose a network profile or set your own latency, response bandwidth and dropped-request rate. Disable HTTP caching and block cookies when you need a fresh, signed-out investigation.

Apply changes explicitly and reset them in one click. Forwarded requests pick up the new conditions; your old captures keep their original timings. Direct Compose sends bypass these controls.

Try the slow-network walkthrough →

Network / Choose the conditionsDESKTOP

Presets, custom values and a clear resetDesktop preview · sample traffic

Mock from a response

Make the next response yours.

Turn a captured response into an editable mock. Its method, exact URL, status, safe response headers and body are already filled in. Change the result, save the draft, and enable it when you’re ready.

Existing rules stay editable. Text, binary and encoded response bytes are preserved; cookies and transport headers are excluded. Exact HTTPS mocks can answer even when the origin is offline.

Try a profile-response mock →

ProxyCat mock editor with an exact POST URL, editable JSON body and the rule disabled until explicitly enabled — A disabled draft, ready for your experimentDesktop preview · sample traffic

Saved captures · Pro

Pick up where you left off.

Name an investigation, keep it on your computer, and reopen it from the desktop library. Import or export a .pcsession file when you want to share the full capture. Opening a session asks before replacing your current traffic.

For a bug handoff, share selected requests as a browser report with notes and privacy controls. Your teammate can inspect the file offline without installing ProxyCat.

See what’s included in Pro →

ProxyCat saved-capture dialog with a named investigation and open, delete, import and export controls — Keep, reopen and share investigationsDesktop preview · sample capture

Share investigations · Pro

Select the requests that explain a bug, add reproduction notes, and export one HTML file. The recipient can search, sort, and inspect headers and any included text bodies in a browser.

Query values and URL credentials are removed; most header values are hidden and bodies stay out by default. Review paths and notes before sharing. No cloud upload or recipient account required.

Open a sample investigation →

ProxyCat sharing dialog with selected requests, reproduction notes, redacted URLs and optional body inclusion — From QA to a developer, with the evidence attachedWorking report · sample traffic

Interactive Demo

Try ProxyCat right here. No download, no account.

A simulated capture session built from sample traffic — nothing leaves your browser. Follow a debugging walkthrough or explore freely. Rules and throttles preview their effect on this sample session; they don’t change an existing capture in the desktop app. The console shows the equivalent local REST calls.

Ready · choose a walkthrough

Play a short walkthrough, or advance one step at a time.

Illustrative sample traffic · finite playback · pause or explore at any time · no network requests are sent

Explore the individual tools

Guided tour · 5 steps

Inspector

Select a request

Rewrite rules /api/Tools/rewrite

Throttle /api/Tools/throttle

Filters /api/ProxyApi/filters

API console every click is one curl

0 calls

TLS and mobile setup

Keep upstream validation on by default, install the local CA only where you intend to inspect, and follow platform-specific mobile guidance.

Validate upstream TLS

Import existing certs (.p12 / .pfx)Cert Viewer

Mobile onboardingiOS / Android

Guided first launch

The tour points at the live controls so new users can capture traffic, trust certificates, and open settings without hunting.

Search and filter

How It Works

From download to first captured request in 60 seconds.

1

Download & Run

One binary. Double-click to launch. No installer, no Java runtime, no Docker required. The proxy starts automatically on port 8888.

2

Point Your Traffic

Set localhost:8888 as your HTTP proxy. Works with browsers, mobile apps, React, Node, Python — anything that speaks HTTP.

3

See Everything. Automate Anything.

Every request appears instantly in the desktop app. Then automate — create rewrite rules, throttle profiles, and filters via the REST API. No clicking required.

Built for repeatable investigations

Inspect, reproduce, and automate your HTTP workflows.

Inspect the exchange in the workbench, keep the evidence, and turn the same setup into a repeatable test. Use the desktop for exploration and the REST API for automation.

SSL/HTTPS Interception

Inspect HTTP/HTTPS with your own local root CA. Guided desktop and mobile setup helps you configure clients that support proxying and trust the certificate.

Rewrite Rules Engine

Map Remote, Map Local, header inject/modify/remove, body find & replace, URL rewriting, status code overrides. All via API or GUI.

Network Throttling

14 built-in presets from 56K modem to 5G fiber. Custom latency, bandwidth caps, and packet loss simulation. Test edge cases instantly.

Full-Text Search

Use the full-text REST search to match URLs, headers and request/response bodies. The desktop’s fast view filters narrow traffic by URL, method and status.

Replay & Compose

Open a captured request as a draft, edit its URL, headers and body, or repeat its original bytes. Inspect the response beside your draft; new results join the numbered capture.

Session Management

A desktop library for named captures on Pro. Reopen investigations, exchange .pcsession files, or share selected requests and notes as an offline browser report. Recipients need no installation to review the report.

HAR Export

Export to standard HTTP Archive format. Import into Chrome DevTools, Lighthouse, or any HAR-compatible tool for further analysis.

Slack Alerts & Notifications

Get notified via Slack in real-time when specific patterns appear. Monitor for 5xx errors, slow responses, or custom conditions. Email notifications coming soon.

API-First Architecture

Core proxy workflows exposed via a clean REST API with OpenAPI docs. Script your proxy config in CI/CD, tests, or any language you use.

Bring traffic into your AI workflow

Use MCP to find failed calls, compare response times and spot large responses from your own AI client. Share capture metadata for this app session; keep headers and payloads in the inspector.

See MCP examples →

Four considered themes

Graphite Dark, warm-paper Light, moss-green Forest and deep-blue Aqua. Switch in Settings; your workbench, dialogs and inspectors follow the same palette.

Captures stay on your computer

The account service handles sign-in and licensing. Your desktop captures and local CA stay on your machine. You choose what to export, share or expose to an MCP client.

Choose Your Workflow

One proxy. Explore by hand or automate through the API.

Start with the visual inspector, then use the REST API to repeat your setup in tests and scripts. Availability and limits depend on your plan.

Workflow	In the app	Through the API
Inspect traffic	Browse requests, headers, bodies, and timing	List captured requests and search traffic
Change responses	Create rewrite and mapping rules	Configure rules from your scripts
Test slow networks	Choose a throttling preset	Apply repeatable network conditions
Reproduce a request	Replay a capture or compose a request	Send requests from automated tests
Share a capture	Sessions → Share report	Export selected requests and notes for offline browser review

Already on Charles Proxy or Fiddler?

Point your traffic to localhost:8888, install the root cert once, and your team is capturing HTTPS traffic. Import your Charles .p12 cert if you want to keep the same certificate chain.

Try ProxyCat Free

Your AI workspace, connected

Ask about the traffic.
Keep the full picture in ProxyCat.

Connect your MCP-compatible AI client to the requests you capture locally. Ask it to find failures, compare status codes and timings, or highlight large responses. Open the request in ProxyCat when you need to inspect headers or payloads.

“Show the 5xx requests to api.example.com.”Narrow the capture by hostname and status range.
“Which captured requests took over a second?”Review request durations to find candidates for investigation.
“Compare the latest two POSTs to api.example.com.”Compare their status, timing and response size.

MCP / SAMPLE CAPTURE METADATA

“Show the failed POSTs to api.example.com.”

Capture ID: sample-042
Host: api.example.com
Method / status: POST / 503
Duration: 1,240 ms
Response size: 312 bytes

Illustrative metadata returned by proxycat_list_requests. This is a sample, not a live AI response. The client can inspect an individual capture with proxycat_get_request and check capture state with proxycat_status.

Connect in three steps

Open Connect AI in ProxyCat and choose Enable for this session.
Copy the generated client configuration into a client that supports local stdio MCP servers.
Capture traffic, then ask your client about it. Choose Disconnect to revoke access.

Access is off by default and ends when ProxyCat closes. MCP exposes hostnames, methods, status codes, timestamps, timings and byte counts. URL paths, queries, headers and bodies are omitted. Your AI client may send the shared metadata to its provider. MCP access is read-only; it cannot change rules or send requests.

Built for Automation

If you can write a curl command, you can automate your proxy.

60+ REST API endpoints with interactive Scalar docs. Set up rewrite rules, filters, and throttling in your CI pipeline — no manual clicks, no config files, just HTTP.

Core workflows, one `curl` away

01 Create rewrite rules to redirect, mock, or modify any request in flight
02 Toggle throttle presets to simulate any network condition globally
03 Search captured traffic, export sessions, and pipe into your toolchain
04 Compose and send custom requests — like Postman, from your terminal

Start with localhost examples →

Rewrite

Throttle

Search

Filter

# Serve a local mock instead of hitting production curl -X POST http://localhost:5050/api/Tools/rewrite \ -H "Content-Type: application/json" \ -d '{ "name": "Mock user API", "ruleType": "MapLocal", "urlPattern": "*/api/users*", "localFilePath": "./mocks/users.json", "localContentType": "application/json", "localStatusCode": 200 }' # Response { "id": "a3f1c9e0b2d4", "name": "Mock user API", ... }

Pricing

Start free. Upgrade when your workflow grows.

No credit card. No account. Download and start debugging. Use Free for quick inspections. Pro adds unlimited daily capture, HAR exports, saved sessions and Slack alerts for investigations you need to repeat and share.

Pay once. Keep your eligible version. Renew updates only when you want to.

Free

$0 / forever

Core traffic debugging. No account required.

1,000 requests / day
10 filter rules
All 8 rewrite rule types
All 14 throttle presets
SSL / HTTPS interception
Full-text search & replay
Full REST API access
Read-only MCP for your AI workspace

Pro

$69 / user once

Launch price: $49/user once — save $20.For 60 days after public downloads open.

The daily workbench for developers and QA.

Unlimited requests / day
Unlimited filter rules
One user · up to 3 device activations
12 months of updates included
Keep your eligible version permanently
HAR export for Chrome DevTools
Slack alerts on matching traffic
Session save / load / share
Priority support
Everything in Free

Enterprise

Custom

For teams buying Pro for multiple people or planning a larger rollout.

Everything in Pro
Unlimited stored requests
Negotiated volume discounts
Billing, device and deployment planning

Download

Grab your platform. Start debugging in 60 seconds.

One binary. No installer, no dependencies, no Java runtime. Includes the desktop GUI, embedded server, REST API, and web dashboard. Extract it. Run it. Done.

Windows

x64

Download .zip

macOS

Apple Silicon (M1/M2/M3)

Download .tar.gz

macOS

Intel (x64)

Download .tar.gz

Linux

x64

Download .tar.gz

Linux

ARM64 / aarch64

Download .tar.gz

Docker / Headless / CI

Docker release coming soon · headless server included with desktop downloads

All downloads also include a standalone headless server binary in the server/ subfolder.

Try It Yourself

A capture is the start of an investigation.

Find the failed request

Filter the sample capture to errors, select a request, and inspect its response body to see what went wrong.

Explore the traffic inspector →

Try a different response

Toggle a demo rewrite rule and compare the result. Watch the equivalent API call appear alongside the capture.

Try a rewrite rule →

Take the evidence with you

Preview and export the sample session as HAR, then use the same workflow with your own captures in ProxyCat.

Preview a HAR export →

Questions

Everything you're wondering, answered.

Is the free tier actually free, or is this a "free trial"?

Actually free. No time limit, no credit card, no account required. Download the binary and use it forever. The free tier includes all core features — SSL interception, all rewrite types, all 14 throttle presets, full-text search, replay, compose, and full REST API access. The free tier is limited to 1,000 captured requests/day and 10 filter rules; HAR export, session save/load, and Slack alerts are Pro features.

What happens when my included updates end?

Your eligible purchased version keeps its Pro features permanently. New releases dated after your update cutoff need an optional $39 renewal, which adds 12 months from your current cutoff or the renewal date, whichever is later. There is no automatic renewal. One license covers one person and three device activations; teammates need their own licenses. Start with Free to evaluate the core workflow.

Why use an API-driven proxy?

ProxyCat combines a visual traffic inspector with 60+ REST API endpoints. Inspect requests in the app, then script your filters, rewrite rules, and throttling for repeatable tests. Self-contained downloads include the runtime, and headless mode supports automation without opening the desktop app.

How do I switch from Charles Proxy?

Download the binary, run it, set your browser or device proxy to localhost:8888, and install the root certificate once. If you're using Charles certificates in your app, you can import your existing .p12 file via the Cert Viewer. Your filters and rewrite rules are JSON — version-control them from day one.

What about mitmproxy? I'm used to scripting my proxy.

mitmproxy's Python addon system is powerful but forces you to write and maintain proxy code in a specific runtime. ProxyCat exposes everything via a clean REST API — use any language, any tool, any CI platform. Run rewrite rules in your test suite with two curl commands. No Python environment to manage, no addon reload cycle. Every desktop download also includes a standalone headless server; a public Docker release is planned.

Can I use it in my CI/CD pipeline?

Absolutely. Every download includes a headless server binary you can run without a GUI. A public Docker image is planned. Set up rewrite rules, filters, and throttle profiles with curl commands in your pipeline scripts. Teams use it to mock external APIs in integration tests and simulate network failures. Pro features on a server (HAR export, unlimited captures) come from a licence you create on your account page — Use Pro on a server or in CI — and pass as PROXYCAT_LICENSE. Each server or CI job uses one of the three device activations included with that individual user's license. A perpetual license keeps eligible releases in Pro permanently; reissue it after renewing updates to include the new cutoff.

Does it work with HTTPS / mobile apps?

ProxyCat generates a local root CA on first launch. Configure the device’s HTTP proxy and install and trust that CA for HTTPS inspection. Desktop browsers and Android/iOS clients that honor the proxy and trust the CA are supported; certificate-pinned apps and clients that ignore system proxy settings need app-specific configuration. Guided setup explains the platform steps.

What happens when I hit the free tier limits?

At 1,000 captured requests in a day, new requests stop being captured but the proxy keeps forwarding traffic normally — nothing breaks. Your existing captures, search, and REST API all keep working, and the counter resets at midnight UTC. No forced upgrades, no nag screens. Upgrade to Pro when (and if) you need unlimited.

Can my team share proxy configurations?

Yes. Rewrite rules and filter sets are plain JSON on every plan — read them from the API or version-control the files in your data directory alongside your test suites. Pro includes full .pcsession file exchange and selected-request HTML reports for offline browser review. Reports hide most header values and all query values; bodies are optional and aren't automatically redacted. There is no hosted workspace or access-controlled sharing link yet. Pro licenses cover one person each; contact sales for negotiated volume pricing if you're buying for a team.

Your HTTP traffic shouldn't be a black box.

Inspect what your app sends, change what comes back, and reproduce the bug. Start with the free tier. No account or credit card required.

View release availability

View Pro availability →

See the request. Find the problem.

Follow a request all the way through.

Change the input. See what happens.

Find what changed between failure and success.

Test the slow connection before your users do.

Make the next response yours.

Pick up where you left off.

Send the evidence. Keep the context.

TLS and mobile setup

Guided first launch

Download & Run

Point Your Traffic

See Everything. Automate Anything.

SSL/HTTPS Interception

Rewrite Rules Engine

Network Throttling

Full-Text Search

Replay & Compose

Session Management

HAR Export

Slack Alerts & Notifications

API-First Architecture

Bring traffic into your AI workflow

Four considered themes

Captures stay on your computer

Ask about the traffic.Keep the full picture in ProxyCat.

Connect in three steps

Core workflows, one curl away

Docker / Headless / CI

Find the failed request

Try a different response

Take the evidence with you

A debugging tool you can keep.

Is the free tier actually free, or is this a "free trial"?

What happens when my included updates end?

Why use an API-driven proxy?

How do I switch from Charles Proxy?

What about mitmproxy? I'm used to scripting my proxy.

Can I use it in my CI/CD pipeline?

Does it work with HTTPS / mobile apps?

What happens when I hit the free tier limits?

Can my team share proxy configurations?

See the request.
Find the problem.

Ask about the traffic.
Keep the full picture in ProxyCat.

Core workflows, one `curl` away