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jlink-mcp

by Klievan
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rtt_read

Read RTT log lines from embedded devices via J-Link, returning newest messages by default or oldest boot output when requested. Reading does not consume the buffer.

Instructions

Read RTT log lines (clean, parsed Zephyr format). Non-destructive — reading does not consume the buffer. Returns the NEWEST lines by default; oldest:true returns the start of the buffer. Note the buffer spans reflashes: its oldest lines may be from firmware you have since replaced. rtt_clear drops them.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
countNoHow many lines (default 50)
oldestNoReturn the OLDEST lines instead of the newest — use this to see boot output

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.7.0
    • changedInput schema / properties / count / description
      Previous value: -"Lines to read (default 50)"New value: +"How many lines (default 50)"
    • addedInput schema / properties / oldest
      Added value: +{
+  "description": "Return the OLDEST lines instead of the newest — use this to see boot output",
+  "type": "boolean"
+}
  2. First observedv0.3.2

TDQS

A4.5/5.0
Behavior5/5

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

With no annotations provided, the description carries the full behavioral disclosure burden. It explicitly states non-destructive behavior, the default newest-line ordering, the oldest:true behavior, and the reflash-spanning caveat. This is substantial transparency for a read operation.

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?

Four sentences, each contributing distinct value: purpose, non-destructive behavior, ordering semantics, and reflash caveat. It is slightly longer than strictly necessary but every sentence earns its place and the key information is front-loaded.

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

Completeness4/5

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

For a two-optional-parameter read tool with no output schema and no annotations, this description is quite complete. It covers return orientation, buffer persistence, and the destructive counterpart. It does not mention prerequisites such as an active RTT connection, but that is a minor gap given the tool's simple scope.

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. The description adds meaning beyond the schema by explaining the default ordering ('Returns the NEWEST lines by default'), the practical use of oldest, and the reflash caveat tied to the oldest lines. It does not add much about count, but the existing schema already documents it well.

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 clearly identifies the tool as reading RTT log lines and specifies the format ('clean, parsed Zephyr format'). It also differentiates the behavior from related tools by explicitly noting non-destructive reading and referencing rtt_clear as the operation that drops lines.

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

Usage Guidelines4/5

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

The description provides clear context for when to use the tool: reading RTT logs without consuming the buffer, with oldest:true for boot output. It does not explicitly enumerate alternatives or exclusions, but the mention of rtt_clear and the buffer semantics gives practical routing 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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