I built the tool StackOne's CEO said every developer needs

I wasted 30 minutes debugging my AI agent last month.

Stepped through the orchestration code, checked the prompt,
added console logs everywhere. Turns out the tool call itself
was failing. The agent had nothing to do with it.

Wrong BambooHR subdomain. Silent redirect. isError: false.
Classic.

StackOne's CEO posted about this exact problem — test your
tools via RPC before wiring into your agent. There's no easy
visual tool to do that. So I built one.

The 3 bugs that motivated this

Bug 1 — Accept header
StackOne's MCP server requires both application/json and
text/event-stream in the Accept header. Miss one and it
rejects the connection before processing anything.

Bug 2 — Silent BambooHR failure
isError: false and HTTP 200 — but the employee never
appeared. Wrong subdomain connected in StackOne. The response
was a redirect, not a creation. Always verify in the target
system, not just the response code.

Bug 3 — Wrong Slack tool name
I assumed slack_post_message. StackOne uses
slack_send_message. Never assume tool names match the
provider API. Always call tools/list first.

What I built

StackOne Agent Playground — 4 features, one goal: test
everything before your agent touches it.

RPC Tool Tester
Select integration, pick tool from auto-loaded list, fill
arguments, fire. See full response with isError badge and
latency. No more guessing tool names.

Token Visualizer
Full tool loading = 14,280 tokens. After Tool Discovery =
840 tokens. 94% reduction. Live bar chart with real numbers.

Workflow Simulator
4-step onboarding workflow — Greenhouse and BambooHR mock,
Notion and Slack live. Real pages created, real Slack messages
sent. Full audit trail per step.

Defender Tester
Paste any tool response, scan for prompt injection. Highlights
exact flagged phrases and explains the attack pattern.

One bug I hit building this

// This throws a runtime error in Vite
import { ToolCallResult } from '../types'

// This is correct — interfaces are type-only
import type { ToolCallResult } from '../types'

Classic TypeScript + Vite gotcha. import type tells Vite
the import is for type-checking only, not runtime.

Try it

git clone https://github.com/prathyushak828/stackone-agent-playground
cd stackone-agent-playground
npm install
cp .env.example .env
npm run dev

No backend. Mock mode works without any credentials.

GitHub: https://github.com/prathyushak828/stackone-agent-playground

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