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

Goes well beyond the annotations: the tool is a no-op that ignores arguments, stores nothing, and only returns a sign-up link, and no authentication is required anywhere. It also discloses the real key-acquisition workflow and header name, which the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false) cannot convey. The readOnlyHint=false flag nominally implies side effects while the description says nothing is stored, but readOnlyHint=false is the non-assertive default and the description correctly warns the agent away, so this is informative rather than misleading.

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 single most decision-relevant word ('Deprecated') and then packs deprecation reason, actual behavior, routing to alternatives, and the correct auth path into four tight sentences. Nothing is redundant with the annotations, and no sentence could be dropped without losing a decision input.

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 zero-required-parameter, no-output-schema tool, the description covers everything an agent needs: current behavior, absence of side effects, whether a key is needed, where to get one, and which siblings to use instead. It even explains the return value (a sign-up link) in the absence of an output schema.

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 says 'Ignored — kept for backward compatibility'. The description adds tool-level closure by stating that the tool 'ignores its arguments', so an agent knows no argument combination changes the outcome and none need be constructed; that is meaningful beyond the per-field notes, though no format or syntax detail is added.

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 exactly what the tool is ('Deprecated: returns a sign-up link instead of creating an API key, ignores its arguments and stores nothing'), which is a precise verb+resource+outcome statement. It also distinguishes itself from siblings by naming get_signals and get_stats as the tools that actually work without a key.

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?

Explicit when-not-to-use ('Don't call it to get access') plus the correct alternative path (create keys at the signup URL and send them via the X-Api-Key header). It even explains why it still exists ('Kept only so older clients don't break'), so the agent knows the call is only warranted for legacy compatibility.

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