23-tool developer Swiss army knife via mcp-devtools-server — cron explain, JSON diff, HTTP status, byte convert, hash, HMAC, JWT, QR, regex, base64, color, and more (npx)

Recipe: 23-tool developer Swiss army knife via mcp-devtools-server

Server: mcp-devtools-server v1.0.1 Transport: stdio Install: npm install mcp-devtools-server then node dist/index.js Auth: none (zero API keys)

Tools (23)

NOVEL TOOLS (not covered by single-purpose MCP servers)

cron_explain — explain cron expressions

→ cron_explain({expression: "0 0 * * MON-FRI"})
← "Minute: 0 → at 0, Hour: 0 → at 0, Day of Month: * → every value, Month: * → every value, Day of Week: MON-FRI → range MON-FRI"

→ cron_explain({expression: "*/5 * * * *"})
← "Minute: */5 → every 5 minute(s), Hour: * → every value, ..."

→ cron_explain({expression: "garbage"})
← "Error: Expected 5 or 6 fields (minute hour day month weekday [year])"

json_diff — structural JSON comparison with JSONPath

→ json_diff({a: '{"name":"Alice","age":30}', b: '{"name":"Alice","age":31}'})
← "Found 1 difference(s): $.age: 30 → 31"

→ json_diff({a: '{"a":1,"b":2}', b: '{"a":1,"c":3}'})
← "Found 2 difference(s): $.b: 2 → (missing), $.c: (missing) → 3"

→ json_diff({a: '{"deep":{"a":{"b":1}}}', b: '{"deep":{"a":{"b":2}}}'})
← "Found 1 difference(s): $.deep.a.b: 1 → 2"

http_status — HTTP status code lookup with categories

→ http_status({code: 418}) → "418 I'm a Teapot ☕ — Client Error (4xx)"
→ http_status({code: 429}) → "429 Too Many Requests — Client Error (4xx)"
→ http_status({code: 503}) → "503 Service Unavailable — Server Error (5xx)"
→ http_status({code: 999}) → "999 Unknown status code — Server Error (9xx)"

byte_convert — SI + binary byte unit conversion

→ byte_convert({value: "1GB"})
← "Bytes: 1,000,000,000 B | KB: 1000000 | MB: 1000 | GB: 1 | TB: 0.001 — KiB: 976562.50 | MiB: 953.67 | GiB: 0.9313"

→ byte_convert({value: "1GiB"})
← "Bytes: 1,073,741,824 B | KB: 1073741.82 | MB: 1073.74 | GB: 1.0737 — KiB: 1048576 | MiB: 1024 | GiB: 1.0"

Correctly distinguishes SI (KB=1000) vs binary (KiB=1024).

KEY GOTCHAS

1. ⚠️ `base64_decode` param is `encoded` NOT `text` — using text causes validation error
2. ❌ `timestamp` tool is BROKEN — ignores the value parameter entirely, always returns current time regardless of input
3. ❌ `number_base` `from` param is BROKEN — ignores the source base, always treats input as decimal. "ff" from=16 → "Error: Could not parse number"; "10" from=2 → returns 10 decimal (should be 2)
4. `cron_explain` is field-by-field — does not produce a full English sentence like "At 9:00 AM on the 1st of every month"
5. `json_diff` uses `$` JSONPath notation for paths (e.g., `$.deep.a.