list_instances

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered by structured data. The description adds real content beyond that by disclosing what the result contains (the default instance, per-instance write-login capability), which annotations cannot express.

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?

A single front-loaded sentence with the resource first and the two returned attributes immediately after. Nothing is redundant or restates the tool name.

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?

An output schema exists, so per-field return documentation is unnecessary, yet the description still pre-summarizes the two most decision-relevant fields. For a zero-argument, read-only listing tool with rich annotations, nothing an agent needs in order to call it correctly is missing.

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?

The input schema has zero properties, so there is no parameter semantics to explain; the baseline for a no-parameter tool is 4. The description correctly implies the call takes no arguments by describing only the resource being listed.

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?

States a specific verb ('List') and resource ('configured Hydra instances') and goes further by naming the two facts returned about each: which one is the default and whether it can log in for write tools. No sibling (cancel_build, get_project, list_evals) overlaps with Hydra instance discovery, so it is unambiguously distinct.

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 phrase 'whether each can log in for write tools' implies a pre-flight use case — checking write capability before invoking a mutating tool — but the description never says when to call this versus just calling a write tool, nor does it state any prerequisites or exclusions. Usage must be inferred rather than read.

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