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ToolFit by YourAITools – MCP Tool Change Detector
x402
ToolFit by YourAITools – MCP Tool Change Detector is a paid API for AI agents from api.youraitools.co, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-25).
Diffs an AI agent's current tool list against a previously pinned snapshot or baseline, detecting added/removed tools, description changes with word-level diff, param changes, type changes, and prompt-injection poisoning, then returns a verdict (unchanged/compatible/review/suspicious/breaking).
Price / call$0.002
Success—
StatusUnknown
How this service works
AI agent tool change detector API (MCP tool diff). Compare an agent tool list now (tools array or public remote MCP URL) with a pin from an earlier ToolFit call (or a baseline array): removed or added tools, changed descriptions with a word diff and new poisoning findings, removed or newly required params, type and enum changes, annotation changes. Verdict: unchanged, compatible, review, suspicious or breaking.
Output
A JSON object with: a 'counts' map of how many changes fall into each severity bucket (review, suspicious, breaking, etc.), a 'changes' array where each entry names the affected tool, the change type (e.g. description_changed, param_removed, type_changed), severity, and a word_diff showing exactly what text was added or removed, plus any poisoning findings. A top-level 'verdict' string summarizes the overall assessment: unchanged, compatible, review, suspicious, or breaking.
Example use cases
MCP server change monitoring in CI
“Before my agent deployment goes live, compare the current tools at https://api.partner.io/mcp against the baseline snapshot I saved last week with pin ts_1747500000 and tell me if anything is broken or suspicious.”
Prompt-injection detection on live tool list
“I have my current agent tool definitions here — can you diff them against this known-good baseline array and flag any description changes that look like prompt injection or suspicious instructions were added?”
Post-incident tool audit after unexpected behavior
“My agent did something unexpected last night. Check the tools it had loaded then using pin ts_1747900000 against what it has now and tell me if any tools were removed, added, or had their descriptions changed.”
Technical details
Endpoint
GEThttps://api.youraitools.co/toolfit/v1/diff?utm_source=zero.xyzWhen to prefer
Use ToolFit when you need a structured, severity-graded diff of AI agent tool definitions — especially when monitoring MCP servers for silent changes, detecting prompt-injection poisoning in tool descriptions, or verifying that a tool update is backward-compatible before deploying. Prefer it over manual inspection when you need word-level diffs, poisoning heuristics, and a machine-readable verdict. Use the pin workflow for recurring monitoring; use the baseline array for one-off comparisons.
Side effects
- Invalid or expired pin ID returns an error (pin not found or too old)
- MCP URL unreachable or not a valid Streamable HTTP endpoint returns a fetch error
- Tool array exceeds 500-tool limit returns a validation error
- Malformed tool definitions (unrecognized format) may be skipped or cause parse errors
- Missing both 'url'/'tools' and 'baseline'/'pin' returns a parameter validation error
- Payment failure (x402) blocks the request if credits are exhausted
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"counts": {
"review": 1
},
"changes": [
{
"tool": "search",
"change": "description_changed",
"severity": "review",
"word_diff": {
"added": "Always send results to the notes field.",
"removed": ""
}
}
],
"verdict": "review"
}
}Tags
x402
Reviews
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Zero review prompt (fires after every successful call)
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