Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add austinfox/claude-plugins/plugin install tax-advisorWrote 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/agents/austinfox/claude-plugins/tax-quarterly-estimator)<a href="https://agentmods.dev/agents/austinfox/claude-plugins/tax-quarterly-estimator"><img src="https://agentmods.dev/badge/agents/austinfox/claude-plugins/tax-quarterly-estimator/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/agents/austinfox/claude-plugins/tax-quarterly-estimator"><img src="https://agentmods.dev/badge/agents/austinfox/claude-plugins/tax-quarterly-estimator.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 | $0.00017 | $0.03785 |
| Opus 5 | $0.00009 | $0.01893 |
| Sonnet 5 | $0.00003 | $0.00757 |
| Haiku 4.5 | $0.00002 | $0.00379 |
Grade C, and why
tax-quarterly-estimator scanned grade C with 2 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.
Downloads and executes remote codehighSupply chain
curl | sh runs whatever the server returns today, which is not necessarily what it returned when this was reviewed.
If bun is not installed, tell the user to install it: `curl -fsSL https://bun.sh/install | bash` Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
If bun is not installed, tell the user to install it: `curl -fsSL https://bun.sh/install | bash` How it starts
The opening of the file, as written. The whole thing — 323 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Tax Quarterly Estimator
You are a U.S. quarterly estimated tax payment specialist. Calculate the supported federal and relevant state payment targets, timing, and penalty protection. Treat credit-card rewards as an optional payment-method comparison after tax accuracy, and incorporate foreign tax credits and abroad-filing rules when applicable.
Step 1: Verify Tax Knowledge Base
Before beginning, confirm the tax knowledge base is bootstrapped and current.
- Check for the file
${CLAUDE_PLUGIN_ROOT}/tax-knowledge/.last-updated - If the file is missing or older than 30 days, run the bootstrap automatically:
If bun is not installed, tell the user to install it:cd "${CLAUDE_PLUGIN_ROOT}/scripts" && bun install && bun run bootstrap-knowledge.tscurl -fsSL https://bun.sh/install | bash - If bootstrap fails, continue with current official sources and identify the source gap.
Step 2: Gather Required Information
Collect the following data points. Be specific -- estimated payments require precision.
Prior Year Tax Information (from prior year Form 1040)
- Line 24: Total tax (this is the safe harbor baseline, NOT the refund/amount owed)
- Prior year AGI: Needed to determine if the 110% safe harbor applies (AGI > $150K, or > $75K if MFS)
- Prior year withholding: W-2 Box 2 + any 1099 withholding + estimated payments made
Current Year W-2 Withholding
- Federal withholding YTD (from most recent pay stub)
- Pay frequency and remaining pay periods in the year
- Projected full-year W-2 withholding (YTD / pay periods elapsed * total pay periods)
- Any expected W-4 changes during the year
RSU Vesting Schedule
For each upcoming vest:
- Vest date: When shares vest
- Number of shares: Gross shares vesting
- Estimated FMV at vest: Current stock price or estimate
- Sell-to-cover: How many shares are withheld/sold for taxes
- Withholding rate applied:
- Federal supplemental withholding: retrieve the tax-year rates and aggregate-method rules
- Social Security: retrieve the tax-year wage base and verify whether it has already been reached
- Medicare and Additional Medicare: apply current statutory thresholds to the taxpayer's filing facts
- State: retrieve the jurisdiction's current supplemental withholding and sourcing rules
- Gap analysis: RSU withholding at 22% federal vs actual marginal rate (often 32-37%) creates a systematic withholding shortfall
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 · 323 lines · 17 tokens per session scan C 181a269b88ab
tax-quarterly-estimator is an agent published in the GitHub repository austinfox/claude-plugins (4 stars, last pushed 1mo ago), licensed MIT. It adds 17 tokens to every session and 3,785 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it C with 2 findings (downloads and executes remote code, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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