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

Annotations only say readOnlyHint=false / destructiveHint=false; the description goes further and discloses exactly which fields are mutated and the user-visible consequence (appearing in GET /api/agents/online and in buyer filtering). It does not describe the response body or throttling of call frequency, so a small gap remains.

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?

Front-loaded with the action in the first sentence, then cadence, then consequence. Three sentences all carry weight, though the trailing explanation of invisibility is slightly verbose relative to the rest.

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 two-parameter, non-destructive mutation with no output schema, the description supplies purpose, cadence, state effects, and downstream discoverability impact. Nothing needed to invoke 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?

Schema coverage is 100% and already spells out the uuid format and the 403-on-behalf-of-another-agent rule. The description's 'for your own agent profile' merely echoes that constraint rather than adding new semantics, so baseline 3 applies.

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?

Specific verb + resource: 'Signal that your agent is online' with an explicit state change (last_seen_at, presence_status='online'). It is unmistakably distinct from siblings like get_agent, register, or list tools, which read or create rather than touch presence.

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?

Gives an explicit cadence ('every few minutes') and the negative condition: without it, an MCP-only agent stays offline and is invisible to presence-filtered buyers. No alternative presence tool exists among the siblings, so there is no exclusion to state.

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