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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false, and openWorldHint=true, so the safety profile is covered. The description usefully adds that no submission to the employer occurs, which is real behavioral context, but it says nothing about repeat calls (despite idempotentHint=false) or what happens if the vacancy was never applied to.

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?

Two short sentences, zero filler, with the core action stated first and the most dangerous misreading (that this submits an application) corrected immediately after.

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 full schema coverage and annotations that declare the mutation profile, the description covers what an agent needs to select and call it. The only mild gap is behavior on repeated or invalid calls, which matters given idempotentHint=false.

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% with a single required 'slug' parameter whose schema description points to the vacancy's public_slug. The description adds no meaning beyond that, so the baseline of 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?

The description gives a specific verb and resource ('Mark a vacancy as applied to') and immediately clarifies the crucial scope boundary: this records the user's own application rather than submitting anything. That separates it from the auto_apply_* siblings in spirit, though it never names save_job/track_job/auto_apply_start explicitly.

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?

Usage is implied rather than stated: the second sentence tells the agent this is for applications the user already made themselves, which is meaningful routing guidance away from auto_apply_* tools. There is no explicit 'use this when / use X instead when' statement or mention of prerequisites.

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