dsh-tool-calculator

中文

DSH Calculator tool plugin — a safe mathematical expression evaluator. Zero dependencies, zero processes, pure functions.

Motivation

Agents being unreliable at arithmetic is a common weakness of LLMs. DSH's built-in bash tool can call echo $((15 + 27 * 3)) to do calculations, but it has two problems:

1. Every arithmetic operation spawns a bash process — especially expensive on Windows (process creation, shell loading, execution, output collection), with noticeable cumulative latency under high-frequency calls
2. bash arithmetic syntax is limited — it doesn't support math functions such as sqrt, sin, cos, log, pow; in these scenarios the agent can only guess the answer or write a script

This plugin provides a zero-dependency, zero-process, pure-function calculator — a single function call returns the result in milliseconds, covering common elementary math functions.

Security Model

No eval, no new Function. It uses a hand-written recursive descent parser (lexer layer + parser layer), evaluating only whitelisted nodes:

• The lexer layer only recognizes numeric literals, whitelisted identifiers, and operators; quotes, semicolons, backticks, {} [] fail directly with an error
• Identifiers are looked up by name in the whitelist table (15 functions + 2 constants); anything not found throws Unknown identifier
• Evaluation results must be finite numbers; NaN/Infinity (division by zero, square root of a negative number, etc.) are uniformly rejected

new Function + regex whitelisting is unsafe — constructor.constructor(...) can reach the Function constructor directly and execute arbitrary code, and process.exit(0) can kill the host process outright (both reproduced in actual testing). This implementation uses no code-evaluation shortcuts.

Architecture

┌──────────────────────────────┐
│         DSH Agent             │
│  tool call: calculator { ... }│
└──────────┬───────────────────┘
           │ ctx.tools.register()
┌──────────▼───────────────────┐
│     src/index.ts             │
│     Cordis 插件入口           │
└──────────┬───────────────────┘
           │
┌──────────▼───────────────────┐
│     src/evaluate.ts          │
│     tokenize() → parse()     │
│     递归下降解析器            │
└──────────────────────────────┘

• src/index.ts: Cordis plugin entry (name/inject/apply), registers the calculator tool
• src/evaluate.ts: evaluate(expression: unknown): number — the entry point independently validates the type (throws calculator: expression must be a string for non-strings), returns finite numbers, and throws on all invalid input

Tool Declaration

import type { Context } from '@deepseek-ai/cordis'
import { defineTool } from '@deepseek-ai/dsh-tools'
import { evaluate } from './evaluate.ts'

export const name = '@deepseek-ai/dsh-tool-calculator'
export const inject = ['tools']

export function apply(ctx: Context): void {
  ctx.tools.register(defineTool({
    name: 'calculator',
    description:
      'Evaluate a mathematical expression safely. ' +
      'Supports +, -, *, /, %, **, parentheses, and functions: ' +
      'abs, ceil, floor, round, max, min, sqrt, pow, log, log2, log10, exp, sin, cos, tan, PI, E.',
    parameters: {
      expression: {
        type: 'string',
        required: true,
        description: 'Mathematical expression, e.g. "15 + 27 * sqrt(9)"',
      },
    },
    output: {
      schema: { type: 'number' },
      render: (_args, value) => [{ type: 'text', text: String(value) }],
    },
    execute: async (args) => evaluate(args.expression),
    timeoutMs: 1000,
  }))
}

Supported Operations

Precedence: ** (right-associative) > unary ± > * / % > + -.

DSH 0.1.5-rc.1 Compatibility (Verified)

This plugin has been migrated to the DSH 0.1.5-rc.1 harness and fully verified end-to-end in an isolated consumer of local harness 0.1.5-rc.1:

• Types/runtime: @deepseek-ai/cordis: ^4.0.1 + @deepseek-ai/dsh-tools: >=0.0.1-rc.1 <0.2.0 + @deepseek-ai/dsh-invariants: >=0.0.1-rc.1 <0.2.0 (peer); no longer depends on unscoped cordis
• Standalone build: npm install (devDependencies self-contained: typescript/vitest/@types/node) → npm run typecheck → npm test → npm run build → npm pack
• Consumption verification: tarball loaded into a 0.1.5-rc.1 consumer → dsh --profile compat --dump-config shows this plugin's row → the tool genuinely registers and executes
• Launch method: npx -p @deepseek-ai/dsh@next dsh web (lib production mode; don't install -g globally)

Version Adaptation

• DSH adapted: DSH 0.1.5-rc.1 (migration: profile/bundle plugin system)
• bundle declaration: dsh.bundle in package.json (patch points to cordis.patch.yml) + exports export
• patch format: cordis.patch.yml uses the - insert: list (the DSH 0.1.5-rc.1 patch is id-targeted semantics; a bare - id: entry reports entry not found)
• files: the published tarball contains lib/, src/, cordis.patch.yml

Installation

Profile Bundle (Recommended)

As of DSH 0.1.5-rc.1, this plugin can be installed into any profile as a standalone bundle in one step (repositories live at https://github.com/omdsh-dev, public):

# 交互式（web）profile
dsh plugin --profile web add github:omdsh-dev/dsh-tool-calculator
# 一次性任务（headless）profile —— dsh run 默认使用 headless
dsh plugin --profile headless add github:omdsh-dev/dsh-tool-calculator

You can also pack a tarball with npm pack first and install that:

git clone https://github.com/omdsh-dev/dsh-tool-calculator
cd dsh-tool-calculator
npm install && npm pack
dsh plugin --profile web add ./deepseek-ai-dsh-tool-calculator-*.tgz
dsh plugin --profile headless add ./deepseek-ai-dsh-tool-calculator-*.tgz

The in-package dsh.bundle.patch (pointing to cordis.patch.yml) automatically adds the plugin to the profile's layer stack after installation; the plugin's cordis.patch.yml inserts the tool-calculator entry via - insert:. The plugin's missing peer dependencies (@deepseek-ai/cordis, @deepseek-ai/dsh-tools, @deepseek-ai/dsh-invariants) are provided by the profile's healed profiles/node_modules fallback installation.

⚠️ web and headless are different profiles: installing for web doesn't automatically cover headless; dsh run uses the headless profile by default. Use forward slashes for Windows paths (C:/...).

Verify Installation

dsh --profile web --dump-config | grep tool-calculator

Runtime Verification

dsh run "使用 calculator 工具计算 1+2*3"

Manual Installation (Source Contribution / Legacy Snapshot Scenarios)

For source contribution (developing/debugging this plugin in the monorepo) or for scenarios still using old snapshots:

1. Place it in the monorepo: cp -r calculator ~/.dsh/source/master/packages/tools/calculator (dev debugging)
2. Add "@deepseek-ai/dsh-tool-calculator": "workspace:^" to apps/cli/package.json; add { "path": "./packages/tools/calculator" } to the tsconfig.host.json references
3. pnpm install && pnpm run build
4. Insert the plugin in the profile user-layer patch (~/.dsh/profiles/<name>/cordis.patch.yml):

- insert:
    - id: tool-calculator
      name: '@deepseek-ai/dsh-tool-calculator'

1. Verify: dsh --profile <name> --dump-config | grep tool-calculator

DSH 0.1.5-rc.1 note: the patch is id-targeted semantics — a bare - id: entry reports entry "xxx" not found; it must be wrapped in a - insert: list.

Usage

After installation, the agent automatically gets the calculator tool:

calculator { expression: "15 + 27 * sqrt(9)" }  →  96

The tool name satisfies DeepSeek's function-name constraints (≤64 characters, [A-Za-z0-9_-]). After registration it automatically enters the Code Mode SDK (await tools.calculator(...)), and the canonical return value is a number.

Known Limitations

1. Distribution chain: @deepseek-ai/dsh-tools is now published as a private npm package with DSH 0.1.5-rc.1; the plugin installs directly via dsh plugin add github:omdsh-dev/... or the tarball, with no need to place it in the monorepo for workspace resolution
2. Trigonometric functions use radians: consistent with Math.sin/Math.cos; write sin(30 * PI / 180) when you need degrees
3. No big integers: JS number is an IEEE 754 double; the safe integer range is ±9e15, beyond which precision is lost
4. No scientific notation: 1e5 is rejected by the lexer layer

Testing

pnpm test

Includes functional test cases and attack-payload cases (constructor.constructor chain, process.exit(0), globalThis, quote injection, semicolon statements, etc.). The complete case list is in the locally maintained design document.

License

MIT