agent_register_capability

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

With no annotations, the description carries the full burden and does well: it discloses public visibility, a hard gating prerequisite, and a persistence side effect ('Acts as the identity in the local credential store'). It omits what happens on success/overwrite and whether re-registration replaces an existing capability, which keeps it from a 5.

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 tight sentences with no filler, and the gating prerequisite is surfaced immediately after the purpose. Every clause earns its place.

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 3-parameter write tool with no annotations and no output schema, the description covers visibility, access gating, and the identity-store side effect, which is most of what an agent needs. It leaves the success result and re-registration semantics unstated, so it is strong but not fully complete.

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 100%, so all three parameters are already documented in the schema. The description adds only the notion that the published description is public, which is already implied by the schema; baseline 3 is appropriate.

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+resource ('Advertise a capability') plus the downstream intent ('so other agents can send you tasks'), which distinguishes it from the read-side siblings agent_list_capabilities, agent_search_capabilities and agent_delete_capability. It does not explicitly contrast with the similarly named agent_register, so a small differentiation gap remains.

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 a real usage condition: the operation is refused unless the owner set VOIDLY_MCP_RELAY_ALLOW_OPEN_WRITES=1, so an agent knows when the call is permissible. It stops short of naming alternatives (e.g., use agent_register for identity vs this tool for capabilities), so it is clear context without explicit routing.

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