The free toolkit
for agent builders.
Free, instant and private utilities for LLM apps, tool calling and MCP. No signup, nothing leaves your browser, and your agents can use them too.
{
"mcpServers": {
"agenttoolbox": {
"url": "…/api/mcp"
}
}
}
{
"input_tokens": 1284,
"gpt-4o": 0.0032,
"claude-sonnet": 0.0039
}
✓ 4 tools available
Everything you need.
Nothing you don't.
Know the cost
before you ship.
Paste any prompt and see token counts and per-call and monthly cost across GPT, Claude, Gemini and Llama, side by side.
Open Token & Cost Estimator| Model | Per call | Per month |
|---|---|---|
| GPT-4o | $0.00625 | $6.25 |
| Claude Sonnet | $0.00900 | $9.00 |
| Gemini 1.5 Flash | $0.00019 | $0.19 |
| GPT-4o mini | $0.00038 | $0.38 |
One schema.
Every format.
Turn a JSON Schema into ready-to-paste tool definitions for OpenAI, Anthropic and the Model Context Protocol. Validated as you type.
Open JSON Schema → Tool Definition{
"name": "get_weather",
"description": "Get current weather",
"input_schema": {
"type": "object",
"properties": {
"city": { "type": "string" }
},
"required": ["city"]
}
}Prompts, without
the guesswork.
Catch hedging, conflicting rules, leaked secrets, missing output formats and more, before your agent does something surprising.
Open System Prompt Linter⚠ Hedging language weakens instructions
✕ Possible API key found in prompt
⚠ No output format specified
✓ Role defined
Your agents can use every tool.
A JSON API, an OpenAPI spec, llms.txt and a hosted MCP server. Point your agent at it and go.
curl -X POST /api/tools/estimate_tokens \
-d '{"text":"You are a helpful agent…"}'Developer docs Private by design
Web tools run 100% client-side. Your prompts never touch our servers.
Instant
No logins, no loading spinners. Open a tool and you're working.
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