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

Annotations (readOnlyHint, destructiveHint=false) already declare a safe read, and the description is consistent with and additive to that: it discloses the tool is deprecated, is a no-op that stores nothing, ignores all arguments, and is retained only for backward compatibility. This is exactly the behavioral context annotations cannot convey, and it directly warns the agent away from a misleading name.

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 'Deprecated:' and every sentence carries actionable content (what it does, what not to do, two alternative paths). It is somewhat dense with parentheticals and protocol detail, but none of it is filler given the misdirection risk of 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?

For a deprecated no-op with four inert parameters and no output schema, the description covers everything the agent needs: behavior, absence of side effects, reasons for retention, and the correct path to actually obtain access. No output schema exists, so no return-value explanation is required.

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 every property already carries 'Ignored — kept for backward compatibility', so the baseline is 3. The description reinforces this at the tool level ('ignores its arguments'), confirming that no parameter changes behavior, which is useful signal beyond a per-field note — but it adds no format or syntax detail the schema lacks.

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 opening clause states a specific verb+resource and immediately redefines the actual behavior ('returns a sign-up link instead of creating an API key, ignores its arguments and stores nothing'), which is the opposite of what the name 'register' implies. It names siblings (get_signals, get_stats) and their public behavior, so an agent can place it relative to the rest of the toolset without opening schemas.

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?

Explicitly says when NOT to call it ('Don't call it to get access') and why ('every other tool works without a key'). It then routes the agent to concrete alternatives: in-agent sign-in at the connect URL, or manual key creation plus the X-Api-Key header. Nothing is left to inference.

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