Show HN: DevSnoop

Local Chrome evidence for coding agents

DevSnoop lets Codex, Claude Code, and other coding agents inspect your real Chrome tab, click UI, read console and network failures, catch hard-to-read text and icons, and verify what changed before they edit the wrong file.

Agent debugging cockpit

A tiny product win before install

Prompt

"Click checkout in my local app and tell me why nothing happens."

Agent report

"The UI is clickable. Checkout is blocked by auth. Fix the API/session path before changing the CTA component. Also, the green status text measures 3.3 to 1."

Frontend feedback loop

The missing loop is the browser #

Coding agents are useful when they can check their work. Frontend work breaks that loop because the important evidence is sitting in Chrome: the current DOM, the selected tab, the failed request, the console exception, and the state after a click.

DevSnoop does not replace end-to-end tests or promise that the UI is correct. It gives the agent a local Chrome evidence loop so it can inspect, act, read failures, compare the page, and then decide what code to edit.

Read the loop recipe

Before the edit

• 1 page_summary

finds structure, text, controls, and selectors. - 2 click

orfill

reproduces the real user action. - 3 get_network

andget_logs

explain browser failures. - 4 diff

checks what changed after the action or hot reload. - 5 screenshot

is saved for visual state, layout, and review.

What your agent can do #

Inspect

Semantic page structure, computed styles, element details — condensed for minimal token usage.

Interact

Click buttons, fill forms, scroll pages, hover elements. Your agent drives the browser like a user.

Debug

Console logs, network requests, redacted payloads, JS exceptions — captured automatically, filtered on demand.

Legibility QA

Catch faint text, weak icon contrast, tiny labels, clipping, and gradient cases with selector, location, evidence, and fix guidance.

Control multiple Chrome profiles

Label each DevSnoop profile once, then let your agent list connections and choose the right browser context. Keep separate logins, sites, and test accounts open without mixing their tabs.

How it works #

Agent sends a JSON command via HTTP to the native host running on port 9400

.

Native host forwards the command to Chrome via Native Messaging. The extension executes it on the page.

Structured, token-efficient results flow back the same path. No raw HTML — just what the agent needs.

One HTTP call. Structured results. #

Agents send JSON commands to port 9400

and get back compact, token-efficient responses. No raw HTML. No DevTools protocol.

curl -s -X POST http://127.0.0.1:9400/ \
  -H 'Content-Type: application/json' \
  -d '{"command":"legibility_audit","params":{"viewportOnly":false},"tabID":123}'
{
  "ok": true,
  "result": {
    "score": 84,
    "summary": { "serious": 2, "minor": 1 },
    "issues": [
      {
        "kind": "low_contrast",
        "severity": "serious",
        "element": {
          "textContent": "popular",
          "selector": "nav a:nth-child(3) span",
          "documentRect": { "x": 624, "y": 77, "width": 48, "height": 20 }
        },
        "evidence": { "contrastRatio": 3.61, "requiredRatio": 4.5 },
        "recommendation": "Increase contrast by changing the text color, background color, size, or weight."
      }
    ]
  }
}

Structured browser data stays compact #

A fixed inspect-submit-debug-screenshot workflow shows how much browser context each path sends back to the agent. DevSnoop uses more small calls than Chrome DevTools MCP, but returns denser, task-shaped results with fewer tokens.

See commands

Path	Basis	Calls	Input	Output	Cost
DevSnoop	measured	15	~2.8k text + 2.5k image	~700	~$0.047
Chrome DevTools MCP	measured	7	~4.5k text + 2.5k image	~1.1k	~$0.068
Chrome DevTools CLI	measured	12	~7.6k text + 2.5k image	~900	~$0.078
Screenshot loop	estimated	6	~14.9k image	~1.2k	~$0.111

Costs use gpt-5.5 token pricing estimates. Browser state, page complexity, model choice, and retry behavior change real costs. Screenshot-loop row models six vision turns.

Compare browser agent paths #

DevSnoop is built for local Chrome control when coding agents need selectors, legibility checks, logs, diffs, screenshots, and UI actions without a hosted browser workflow.

One-time $29 license

Closing the frontend loop

Give agents a repeatable browser loop: inspect, act, read failures, diff, then edit.

Capture fetch request bodies

Let agents inspect redacted request and response bodies before editing frontend code.

Browse.dev alternative

Use local Chrome, compact browser commands, and one-time pricing instead of hosted browser sessions.

Chrome DevTools MCP alternative

Give agents page summaries, selectors, diffs, logs, network failures, and screenshots through one local HTTP API.

Works with any coding agent #

Any tool that can make HTTP requests can control the browser.

source & further reading

devsnoop.com — original article