list_services

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable contextual behavior beyond that: the scope semantics (system vs user vs all units) and the environment note that 'Vela runs as user services,' which materially affects correct invocation. No contradiction with annotations.

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

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

Three sentences, zero waste. Purpose is front-loaded, usage guidance follows, and the exclusion with alternative comes last. The parenthetical Vela note earns its place by informing scope selection. Every sentence carries distinct value.

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

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

For a low-complexity list tool with two parameters and no nested objects, the description is nearly complete. It covers purpose, scoping, filtering, and exclusion against get_service_status. Minor gaps: the relationship to the sibling list_failed_services is not clarified (does this tool include failed services?), and the return format isn't described, though 'their status' hints at it.

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

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

Schema description coverage is 0%, so the description must compensate. It fully explains the required scope parameter with explicit valid values ('system|user|all') and their meaning, plus the Vela-specific hint for choosing 'user.' The filter parameter gets only 'narrow results,' which is adequate but leaves matching semantics (by name, status, or both) unspecified.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb+resource+outcome: 'List systemd services and their status.' This clearly states what the tool does and what it returns. It also differentiates from the sibling get_service_status explicitly, so an agent can distinguish the two without inspecting schemas.

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

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

The description gives both positive and negative usage guidance: it explains when to use filter and how to choose scope='system|user|all', and it explicitly states 'Do NOT use to answer whether one specific service is running — use get_service_status instead.' An alternative tool is named with the exact condition that selects it.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.