Borrowing it
Nothing to install: this file belongs to lewing/helix.mcp. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/lewing/helix.mcp/main/.squad/skills/mcp-calltoolfilter-tests/SKILL.mdgit clone --depth 1 https://github.com/lewing/helix.mcpWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/lewing/helix.mcp/mcp-calltoolfilter-tests)<a href="https://agentmods.dev/skills/lewing/helix.mcp/mcp-calltoolfilter-tests"><img src="https://agentmods.dev/badge/skills/lewing/helix.mcp/mcp-calltoolfilter-tests/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/lewing/helix.mcp/mcp-calltoolfilter-tests"><img src="https://agentmods.dev/badge/skills/lewing/helix.mcp/mcp-calltoolfilter-tests.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00027 | $0.00297 |
| Opus 5 | $0.00014 | $0.00148 |
| Sonnet 5 | $0.00005 | $0.00059 |
| Haiku 4.5 | $0.00003 | $0.00030 |
Grade A, and why
mcp-calltoolfilter-tests scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
What it actually says
Context
Use this when validating McpServerOptions.Filters.Request.CallToolFilters, especially filters that mutate inbound CallToolRequestParams.Arguments before SDK parameter binding.
Pattern
- Unit-test the filter by wrapping a capture handler and asserting the request's argument dictionary after the filter runs.
- For binding behavior, wrap
McpServerTool.InvokeAsynccreated from the real attributed tool method; this exercises SDK binding instead of a helper-only path. - Construct
RequestContext<CallToolRequestParams>with a realCallToolRequestParams { Name = toolName, Arguments = ... }and JSON-backedJsonElementvalues viaJsonSerializer.SerializeToElement. - Assert both success routing and failure wrapping: missing required arguments should still become the repo's structured
McpException.
Example Scenarios
- Alias-only argument normalizes before binding.
- Canonical parameter wins when canonical and alias are both present.
- Multiple aliases have documented precedence.
- Non-standard alias casing is accepted when the alias table is case-insensitive.
- Test with realistic value types from telemetry, not just sanitized strings; numeric
JsonElementaliases should be covered when callers send IDs as JSON numbers.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 24 lines · 27 tokens per session scan A 4044ac409e25
mcp-calltoolfilter-tests is a skill published in the GitHub repository lewing/helix.mcp (4 stars, last pushed today), licensed MIT. It adds 27 tokens to every session and 297 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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