Read the mod's heartbeat

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

The description discloses extensive behavioral details: reads off disk, requires no session, returns both sides simultaneously, and explains the data structure nuances (the `clients` list, the `player: null` entry, and how a real client is identified). It explains why it works without a session due to failed launches not storing one. This goes far beyond the readOnlyHint annotation, providing critical context that affects how results are interpreted.

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?

The description is long but well-structured: it leads with the core purpose, then explains the failure context, enumerates the four causes with bullet points, clarifies the `clients` list format, and concludes with rationale for the design. Each sentence adds value, though it could be slightly tightened. The use of bullet points and bolded terms aids readability.

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?

The description is remarkably complete given the tool's complexity. It covers when to use it, what it returns, how to interpret the data (including edge cases like the null player entry), and why it works without a session. The output schema exists but the description adds interpretive context that schema alone cannot provide. Nothing an agent needs 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?

There are zero parameters, so the input schema is trivially 100% covered. The description correctly omits parameter details, and the baseline for zero parameters is 4. No additional explanation is needed, and the description doesn't attempt to fabricate parameter info.

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 clearly states the tool's function: 'Read the mod's heartbeat' and expands on its purpose as the diagnostic for why the game is not answering. It distinguishes itself from siblings by explaining it's the only tool useful when nothing else is and that it reads off disk without a session, unlike other tools that require a session. This makes the purpose unambiguous.

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 explicitly explains when to use this tool: when a launch fails and the error 'no live heartbeat within 300s' is encountered. It contrasts with `launch` which already reads the file but discards the detail, making `heartbeat` the fallback for deeper diagnosis. It also notes it's the only tool useful when nothing else is, giving strong situational guidance.

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