CalDAV MCP Server

Server Quality Checklist

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Latest release: v0.1.0
Disambiguation5/5
Each tool targets a distinct action (create, delete, get, update, search, list calendars, find slots, get free/busy). No overlap; even the two availability tools are complementary.
Naming Consistency5/5
All tools follow the pattern `calendar_verb_noun` with consistent snake_case. Very predictable and clear.
Tool Count5/5
With 8 tools, the surface is well-scoped for a CalDAV server: covers calendar discovery, CRUD, search, and availability checks. Not too many or too few.
Completeness4/5
Event management is fully covered (CRUD + search + availability). However, missing tools for VTODO and VJOURNAL, despite `calendar_list_calendars` reporting them as supported component types.
Average 4.2/5 across 8 of 8 tools scored. Lowest: 3.6/5.
See the Tool Scores section below for per-tool breakdowns.
- No community issues in the last 6 months
- No commit activity data available
- No stable releases found
- No critical vulnerability alerts
- No high-severity vulnerability alerts
- No code scanning findings
- CI status not available
This repository is licensed under MIT License.
This repository includes a README.md file.
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How is the quality score calculated?

The overall quality score combines two components: Tool Definition Quality (70%) and Server Coherence (30%).

Tool Definition Quality measures how well each tool describes itself to AI agents. Every tool is scored 1–5 across six dimensions: Purpose Clarity (25%), Usage Guidelines (20%), Behavioral Transparency (20%), Parameter Semantics (15%), Conciseness & Structure (10%), and Contextual Completeness (10%). The server-level definition quality score is calculated as 60% mean TDQS + 40% minimum TDQS, so a single poorly described tool pulls the score down.

Server Coherence evaluates how well the tools work together as a set, scoring four dimensions equally: Disambiguation (can agents tell tools apart?), Naming Consistency, Tool Count Appropriateness, and Completeness (are there gaps in the tool surface?).

Tiers are derived from the overall score: A (≥3.5), B (≥3.0), C (≥2.0), D (≥1.0), F (<1.0). B and above is considered passing.

Tool Scores

Behavior3/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Given no annotations, the description adds a warning about irreversibility and recurring series handling. However, it omits side effects, required permissions, or response behavior. The output schema exists but its content is not discussed.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is concise, front-loaded with the main action, and structured with a warning and argument list. Every sentence adds value.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness3/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
While the description covers the core operation and a key warning, it lacks context about when to use this tool versus siblings, error conditions, and how the output schema relates. For a delete tool with no annotations, more completeness would be beneficial.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 0% schema description coverage, the description provides meaningful explanations: 'Target calendar name or URL path' for calendar_id and 'UID of the event to delete' for event_uid, which add clarity beyond the schema's titles.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose4/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb ('Delete'), resource ('calendar event'), and identifier ('by its UID'). It also clarifies behavior for recurring events. However, it does not explicitly differentiate from sibling tools like calendar_update_event.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The warning 'This operation cannot be undone' provides caution, and the note about recurring events is helpful. But no guidance on when to use delete versus update or how to delete a single instance of a recurring event.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior2/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries full burden for behavioral disclosure. It mentions return format (list of busy periods) but does not explicitly state it is a read-only operation, discuss required permissions, idempotency, or rate limits. This is a significant gap for a tool that queries calendar data.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness4/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is concise with 5 lines, front-loading the purpose. Every sentence adds value. The args format is clear, though the structure could be slightly improved with consistent bullet style.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness3/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given 3 required parameters, no annotations, but an existing output schema, the description is reasonably complete. It explains return values (list of busy periods) but lacks details on pagination, max time range, or error conditions. For a simple query tool, it meets minimum viability.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 0%, so the description must compensate. It adds meaning for all three parameters: calendar_id as 'Calendar name or URL path', start and end with ISO 8601 format examples. This provides essential guidance beyond the schema's minimal type info.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states it gets busy time slots from a calendar within a time range. It distinguishes from siblings like calendar_find_available_slots by specifying 'busy' instead of 'free'. The verb 'get' and resource 'busy time slots' are specific and unambiguous.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description explicitly says 'Use this to check for scheduling conflicts before creating events.' This provides clear context for when to use. However, it does not mention when not to use or directly compare with alternatives like calendar_find_available_slots.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description takes full responsibility for behavioral disclosure. It states it returns up to 20 sorted slots, explains constraints (working hours/days), and defines search window. It covers the key behaviors for a read-only scheduling tool.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness4/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is front-loaded with a clear purpose sentence, followed by a structured Args block. It is slightly long but no redundant sentences. Every sentence adds value.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given 7 parameters and presence of an output schema, the description covers search constraints and result characteristics (up to 20 sorted slots). It omits the structure of returned slots, but the output schema likely handles that. Still, a brief mention would improve completeness.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 0%, so the description must explain parameters. It lists all 7 parameters with descriptions (e.g., 'ISO 8601 start of search window') beyond the schema titles. However, 'calendar_id' is vaguely described as 'Calendar name or URL path', which could be more precise.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the tool finds available (free) time slots for scheduling new events. This verb+resource purpose distinguishes it from siblings like 'get_freebusy' (which shows busy blocks) and 'search_events' (which finds existing events).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage for scheduling new events but does not explicitly contrast with sibling tools or state when not to use. For example, it doesn't suggest using 'get_freebusy' for checking busy times. The purpose is clear enough for an agent to infer context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided, but the description discloses key behaviors: it creates an event, returns a UID, and advises saving it for future updates/deletion. Parameter details (e.g., timezone default, alarm format) add transparency. Could mention side effects like event creation impact, but overall strong.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness4/5
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is concise and well-structured: a brief opening sentence followed by a clear bulleted list of arguments. Almost all sentences add value, though slight redundancy in repeating parameter names in arguments list.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the complexity (10 parameters, 4 required, no annotations, and an output schema), the description covers all essential aspects: parameter purposes, formats, defaults, and return value. Missing error conditions or limits, but otherwise complete for a creation tool.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters5/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 0% schema description coverage, the description compensates fully by explaining all parameters in detail, including examples for date format, timezone default, RRULE syntax, and alarm_minutes format. This adds significant value beyond the bare schema types.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states 'Create a new calendar event' with a specific verb and resource. Differentiates well from sibling tools like calendar_delete_event and calendar_update_event.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines3/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies when to use (to create an event) but does not explicitly state when not to use or suggest alternatives like calendar_update_event for modifications. Usage guidance is adequate but not explicit.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Describes return fields comprehensively (summary, start/end, description, location, recurrence, attendees, organizer). No annotations, but read-only behavior implied by 'get' verb.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Extremely concise: one-sentence overview, clear Args section, and return summary. No superfluous content.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Covers essential input and output details. Output schema exists reducing burden. Lacks error handling info, but for a simple get tool, it's sufficient.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Adds meaning to both parameters: calendar_id explained as 'name or URL path', event_uid as 'from calendar_search_events'. Schema coverage 0% so description compensates well.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states it retrieves detailed info for a single calendar event by UID. Differentiates from siblings like calendar_search_events (multiple events) and calendar_get_freebusy (availability).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Tells when to use: after getting event_uid from calendar_search_events. Lacks explicit when-not or alternatives but provides clear context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided, so description carries full burden. It discloses the return fields and their types, indicating a read-only listing with no side effects. Lacks detail on potential errors or authentication requirements, but adequate given simplicity.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Three concise sentences: action, return fields, usage guidance. No wasted words, front-loaded with key purpose.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given zero parameters and presence of an output schema (which likely documents return structure), the description fully covers the tool's purpose and usage context.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters4/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
No parameters exist, baseline 4. Description does not need to add parameter info, and the schema coverage is 100% (trivially).
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Explicitly states it lists calendars from a CalDAV server and specifies returned data (name, URL, component types). Clearly differentiates itself from sibling event tools by indicating this is a discovery step.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly advises to use this tool first before searching or creating events, providing clear context. Does not include when-not-to-use or alternatives, but sufficient for a list operation.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Discloses key behavior: 'Only provided fields are changed' (partial update). Lists all parameters with their effects. Missing error conditions and return details, but no annotations to contradict. Good overall transparency.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Structured with concise sentences and an Args list. No wasted words; front-loaded with purpose. Efficient and easy to parse.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness4/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Covers usage hint, partial update behavior, and all parameters with formats. Lacks error handling info and return value description, but output schema likely addresses return values. Very complete given complexity.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters5/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema has 0% description coverage; description fully compensates by explaining all 7 parameters with clear semantics (e.g., 'New event title (omit to keep unchanged)'). Adds significant value beyond schema types.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
Clearly states 'Update an existing calendar event' with specific verb and resource. Distinguishes from siblings like calendar_create_event and calendar_delete_event.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly advises to use calendar_get_event first to see current values, providing clear context for usage. Does not explicitly exclude alternatives but implies proper workflow.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Behavior4/5
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations provided, so description carries full burden. It describes that it returns a list of events with specific fields (UID, summary, start/end, location, status) and explains limit default. No side effects mentioned, but as a search tool, it's reasonably transparent.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Conciseness5/5
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences for summary, then bulleted Args list, then returns, then usage hint. Every sentence earns its place. No redundancy or fluff.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Completeness5/5
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
With 5 parameters (3 required), no nested objects, and an output schema present, the description covers all necessary aspects: parameter explanations, return fields, and how to use results with other tools. Fully adequate for an AI agent to select and invoke correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Parameters5/5
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 0%, so description must compensate. It adds meaning for all 5 parameters: calendar_id (from calendar_list_calendars), start/end (ISO 8601 example), query (optional text search), limit (default 50). This far exceeds the bare schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Purpose5/5
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states 'Search for events in a calendar within a date range' with a specific verb and resource. It distinguishes from siblings like calendar_get_event (single event) and calendar_find_available_slots (available slots).
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Usage Guidelines4/5
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly tells when to use this tool: 'Use UIDs from results for calendar_get_event, calendar_update_event, or calendar_delete_event.' Implicitly indicates it's for searching before acting. Lacks explicit when-not guidance but is clear enough.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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