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disks/performance

Read-onlyIdempotent

Read cumulative block-device I/O counters from /proc/diskstats to measure disk read/write activity; sample twice and subtract to calculate rates.

Instructions

Returns block-device I/O counters from /proc/diskstats: reads and writes completed and merged, sectors (512 bytes) and milliseconds spent, in-flight I/Os and weighted I/O time. Values are CUMULATIVE since boot, not rates and not iostat's per-interval figures; there is no %util or await, so sample twice and subtract to get a rate. Read-only. Without device all devices are listed except loop* and ram*; a name such as sda (find them with disks/list) selects one, and an unknown name gives no such block device. Text output is a table; output_format: json and yaml (real YAML here) return an array of objects with 14 fields (major, minor, device_name, reads_completed, ..., weighted_time_ios_ms). For capacity use disks/free, for SMART health disks/health.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
deviceNoBlock device name such as 'sda' (see disks/list); omit for all except loop* and ram*
output_formatNojson or yaml (real YAML) for structured output; default is a text table

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.4.1
    • changedInput schema / properties / device / description
      Previous value: -"Optional specific block device to query (e.g., 'sda')"New value: +"Block device name such as 'sda' (see disks/list); omit for all except loop* and ram*"
    • changedInput schema / properties / output_format / description
      Previous value: -"Desired output format (e.g. json, yaml, table). Defaults to text"New value: +"json or yaml (real YAML) for structured output; default is a text table"
  2. First observed

TDQS

A4.6/5.0
Behavior4/5

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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered; the description nonetheless adds meaningful behavior: values are cumulative since boot (not rates), no %util or await exist, loop*/ram* are excluded by default, and an unknown device yields 'no such block device'. The one gap is that it never describes pagination or output size limits for the all-devices case, which keeps this from a 5.

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

Conciseness4/5

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

It is dense but front-loaded: the first sentence establishes source and payload, then semantics, then caveats, then alternatives. Almost every clause carries information, though the parenthetical field enumeration ('major, minor, device_name, ...') is slightly over-long for what it conveys.

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

Completeness5/5

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

There is no output schema, so the description must carry return-value semantics itself, and it does: text table by default, JSON/YAML array of 14 named fields, plus cumulative-vs-rate interpretation. Combined with device filtering and error behavior, an agent has everything needed to call and interpret this tool correctly.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3, but the description adds genuine semantics beyond the schema: 'a name such as sda', the exact default-filtering rule (all except loop* and ram*), the error string for an unknown name, and that yaml means real YAML with 14 named fields in JSON/YAML mode.

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 names a specific verb and resource ('Returns block-device I/O counters from /proc/diskstats') and enumerates exactly which counters are returned. It also distinguishes itself from siblings by naming disks/free (capacity), disks/health (SMART) and disks/list (device discovery) as different tools.

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

Usage Guidelines5/5

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

It states when this tool is the wrong choice ('For capacity use disks/free, for SMART health disks/health'), how to obtain a rate (sample twice and subtract), and how to resolve a device name (find them with disks/list). Both the use case and the alternatives are explicit.

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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