units-le-mcp

An MCP server that finds every quantity in a document — a number welded to a unit — and returns it twice: as the document wrote it, and in one base unit so two of them can be compared. Durations come back in milliseconds, sizes in bytes, percentages as a ratio, frequencies in hertz, each with its line, column and key path. It is the engine behind the Units-LE editor extension, exposed as a tool an agent can call.

A quantity it cannot read unambiguously comes back with a named reason, never a guess. A bare 500m is minutes in one config format, milliseconds in another and millicores in Kubernetes, so it is returned as ambiguous_unit rather than as any of them. 1.5KB, 1,5s and 1h + 30m are refused the same way. 1MB is returned as 10^6 bytes, with a flag saying the writer may have meant 2^20. A bare number with no unit is not a finding.

No dependencies, no network calls, no filesystem access. Content goes in, structured results come out.

Use it

Point any MCP host at npx units-le-mcp.

Claude Code

claude mcp add units-le -- npx -y units-le-mcp

Anything with a JSON config — Cursor, Windsurf, Claude Desktop:

{
  "mcpServers": {
    "units-le": {
      "command": "npx",
      "args": ["-y", "units-le-mcp"]
    }
  }
}

VS Code needs nothing here. Install the extension instead — it carries this server and registers it for you: VS Code Marketplace · Open VSX

No Node? The same extract_units tool ships in a static Rust binary: cargo install units-le, then units-le mcp (crates.io). The two servers answer identically — one corpus runs against both, and a differential test feeds both thousands of generated documents in every format, broken ones included, and compares every answer, parser errors and all. The binary additionally offers units_le_scan, which walks a tree; this server reads no files.

Prefer a global install to npx on every launch:

npm install -g units-le-mcp

No environment variables, no API key, no configuration of its own. To check it before wiring it into anything:

echo '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | npx -y units-le-mcp

If that prints the tool name, the server works.

The tool

extract_units

| argument | type | | |---|---|---| | content | string | required. The document text. | | format | json jsonc yaml csv tsv toml ini env | Optional. Anything else, or nothing, scans the text directly. | | filename | string | Used to infer the format when format is absent, e.g. config.toml. | | dimension | duration bytes percent frequency | Report only one. A refusal that names no dimension is always kept. | | maxResults | number | Default 500, from 1 to 5000. |

Refusals are ambiguous_unit, fractional_bytes, locale_separator, compound_arithmetic and out_of_range, each with a sentence a person can act on; si_iec_hazard accompanies a value rather than replacing it. A structured document that does not parse is a diagnostic in its parser's own words, and ok is false while one is present:

{
  "ok": true,
  "data": {
    "quantities": [
      {
        "value": "1h30m",
        "dimension": "duration",
        "baseUnit": "milliseconds",
        "base": "5400000",
        "key": "cache.ttl",
        "line": 2,
        "column": 8
      },
      {
        "value": "500m",
        "dimension": null,
        "baseUnit": null,
        "base": null,
        "reason": "ambiguous_unit",
        "detail": "`m` is minutes in one config format, milliseconds in another and millicores in Kubernetes. Write `min`, `ms`, or spell out the core count.",
        "key": "cpu",
        "line": 3,
        "column": 6
      }
    ],
    "fileType": "yaml",
    "refused": 1
  },
  "diagnostics": [],
  "meta": {
    "tool": "extract_units",
    "count": 2,
    "truncated": false
  }
}

Also in the MCP registry

io.github.nolindnaidoo/units-le — registry.modelcontextprotocol.io

Fifteen more like it

One tool each, same shape: content in, structured data out, no network and no filesystem. Every one is on npm as <name>-mcp and in the MCP registry as io.github.nolindnaidoo/<name>.

| Package | Tool | Does | |---|---|---| | urls-le-mcp | extract_urls | URLs, with protocol and position | | colors-le-mcp | extract_colors | colors from stylesheets and code | | dates-le-mcp | extract_dates | dates and timestamps | | numbers-le-mcp | extract_numbers | numeric values | | paths-le-mcp | extract_paths | file and directory paths | | string-le-mcp | extract_strings | string values | | regex-le-mcp | extract_patterns | regexes, with a ReDoS verdict | | secrets-le-mcp | detect_secrets | credentials, masked — never the value | | envsync-le-mcp | compare_env_files | dotenv key drift, names only | | scrape-le-mcp | analyze_robots_txt | whether a path may be crawled | | unicode-le-mcp | detect_unicode_risks | Unicode that hides meaning, as codepoints | | i18n-le-mcp | check_catalogues | translation catalogues, keys only | | ids-le-mcp | extract_ids | UUIDs, ULIDs and Snowflakes, with the time inside | | ips-le-mcp | extract_ips | IP addresses, CIDR blocks and MACs, normalized | | versions-le-mcp | compare_versions | dependency constraints that disagree across manifests |

Every tool in the family, one page: letools.dev

Built by

Nolin Naidoo — Chief Engineer, AI/ML & Platform Architecture. nolindnaidoo.com · GitHub · LinkedIn

Also from the same workshop

Twelve Rust tools built the same way: small, single-purpose, and driven by a machine rather than a person. pixelcoords and pixelactions make up one loop — pixelcoords answers where, pixelactions acts there. The ten LE crates are the terminal half of the extensions they sit in: the same detection, held to the extension's own corpus, and an exit code instead of a results editor.

| | | | |---|---|---| | pixelcoords | Freeze your screen, mark regions, get pixel-exact coordinates and crops | site · crates.io · docs.rs | | pixelactions | Consume human-verified coordinates, perform the interaction, confirm it landed | site · crates.io · docs.rs | | paths-le | Find every path in a codebase and report whether it still points at anything | crates.io | | secrets-le | Find hardcoded credentials, and never print one | crates.io | | urls-le | Extract every URL from a codebase, with its protocol and exact position | crates.io | | regex-le | Find every regex in a codebase and report which can be driven into catastrophic backtracking | crates.io | | string-le | Get every string in a codebase out where a person can read them | crates.io | | numbers-le | Find every hardcoded number in a codebase so a person can check them | crates.io | | envsync-le | Compare the dotenv files in a tree and say which keys are missing from which | crates.io | | colors-le | Find every colour in a codebase, and say which are not in your palette | crates.io | | dates-le | Extract every date and timestamp, and the exact instant each one resolves to | crates.io | | scrape-le | Check whether a page is scrapeable before the scraper is written | crates.io |

Licence

MIT © Nolin Naidoo