opentax

find_tax_cliffs

Find exact dollar amounts where one more cent of an input costs MORE than a cent of tax (marginal rate over 100%) — e.g. the EITC investment-income kill switch, CTC phase-out steps. Every probe is a real evaluation.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "facts": "<facts>",
      "vary": "<vary>",
      "fromDollars": "<fromDollars>",
      "toDollars": "<toDollars>"
    },
    "name": "find_tax_cliffs"
  }
}

Input Schema

Name	Required	Description
`vary`	Yes	money fact to vary, e.g. "wages" or "taxableInterest"
`facts`	Yes	facts for the computation: either flat corpus fact ids (see list_input_facts) or the same group objects calculate_tax accepts (filing, income, retirement, …), plus optional target and asOf. Business/fiduciary/dependent facts are accepted flat. Unknown keys are rejected by name — nothing is ever silently dropped.
`toDollars`	Yes
`fromDollars`	Yes
`stepDollars`	No	coarse scan step, default 1000; at most 2,000 steps across the range

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 26, 2026

changedInput schema / properties / stepDollars / description

Previous value: -"coarse scan step, default 1000"New value: +"coarse scan step, default 1000; at most 2,000 steps across the range"

addedInput schema / properties / vary / maxLength
```
Added value: +80
```

First observedJul 24, 2026

TDQS

A3.5/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full behavioral burden. It usefully discloses that 'Every probe is a real evaluation,' signaling computational cost, and explains the threshold concept, but it omits return format, side effects, permissions, rate limits, and how step size affects cost or accuracy.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tightly written sentences are front-loaded with the core definition and then examples. Every sentence earns its place, and there is no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

This is a complex search tool with a nested facts object, a dollar range, and a step parameter, and it has no output schema and no annotations. The description explains what a cliff is but does not explain the output shape, how cliffs are reported, boundary behavior, or practical limits, leaving material gaps for correct invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is only 60%, and the description adds no parameter-level semantics for vary, facts, fromDollars, toDollars, or stepDollars. The schema documents some parameters, but the description does not compensate for the undocumented range parameters or explain the facts object shape beyond what the schema already says.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: find exact dollar amounts where one more cent of input costs more than a cent of tax. The marginal-rate-over-100% definition and EITC/CTC examples make it distinguishable from generic tax-calculation siblings like calculate_tax.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The condition for use is implied by 'where one more cent ... costs MORE than a cent of tax' and the examples, but there is no explicit guidance on when to choose this over calculate_tax or other sibling tools, nor any when-not-to-use guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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