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

With annotations already declaring readOnlyHint=false and destructiveHint=false, the description adds genuinely new behavioral context: 'starts no recorder and changes no existing subscription', 'Identical sets converge', and the returned id. There is a mild tension between 'identical sets converge' and idempotentHint=false, but convergence describes a deterministic content-addressed mapping rather than a claim of strict operation idempotency, so it is not a direct contradiction.

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?

Six short sentences, all information-bearing, with the core action front-loaded and the return value and next step following in logical order. The density of domain jargon ('admitted', 'series registry', 'connector digest') costs a little 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?

For a one-parameter tool with no output schema, the description covers what is created, what is deliberately not done (no recorder started, no subscription changed), the exact return value, and the next call to make. An agent has everything needed to invoke it and chain it correctly.

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 0%, so the description must carry the load, and it does: it identifies the parameter as 'bare SHA-256' digests forming an 'admitted' content-addressed set, and warns that a document id is not a registry id. It does not restate the 1-256 cardinality bound, but the semantic meaning is well covered.

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 first sentence gives a specific verb and resource: 'Registers a content-addressed set of admitted document_digests (bare SHA-256)', which is far more precise than the title. It does not explicitly contrast itself with the sibling register_stream_document, so the agent must infer the distinction between registering a set versus a single document.

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?

'Next: start_stream with this registry_id and the exact connector digest and members or series' gives a concrete when-to-use context and the follow-up call, and 'Never infer a registry id from a document id' is a real usage guardrail. There is no explicit when-not/alternative branch, which keeps it short of a 5.

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