MCP Client Compatibility Probe
This server is a diagnostic MCP probe that tests what MCP clients support and how they handle various protocol features.
Inspect client metadata:
echo_metareturns received arguments,_meta, protocol version, client info, and capabilities.Verify structured outputs:
structured_resultreturns both text andstructuredContentmatching a declared schema.Test stateful multi-call workflows:
create_handleanduse_handlecreate and consume explicit handles across calls.Check elicitation/MRTR support:
needs_form_inputrequestsinput_requiredand expects a retry withinputResponses.Verify error handling:
tool_errorreturns a tool-level execution error viaisError: true.Test resource-link content:
resource_link_resultreturns aresource_linkcontent item.Exercise ChatGPT-compatible read-only tools:
searchreturns result IDs/titles/URLs, andfetchretrieves document text.Expose non-tool primitives: the server supports
resources/list,resources/read,resources/templates/list,prompts/list,prompts/get, and a stubsubscriptions/listen.Support both modern discovery and legacy handshake: implements
server/discoverplus a fallbackinitializeresponse.Provide transport neutrality: core logic is transport-independent, with a local
stdioadapter and room for a future HTTP adapter.
Click on "Install Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type
@followed by the MCP server name and your instructions, e.g., "@MCP Client Compatibility ProbeCheck which MCP features you support and report them"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
MCP Client Compatibility Probe
Small diagnostic MCP server for checking what MCP clients actually support.
The server is intentionally dependency-free and split into transport-neutral core logic plus a local stdio adapter. A future HTTP adapter can reuse probe-core.mjs for ChatGPT Web, OpenAI API, or remote MCP testing.
The intended workflow is AI-assisted: point the assistant/client you want to test at this repository and let it run the probe, inspect the trace, create a result file, and prepare a commit. In practice that is a single prompt.
The current informal client support overview lives in CLIENT-MATRIX.md. Detailed test design and result templates live in TESTPLAN.md.
Quick Start For Testers
Option A: One Prompt
Start the assistant or client you want to test, in a directory it is allowed to write to, and give it this:
Clone https://github.com/kascada/mcp-client-compat-probe.git, then read PROMPT.md from that clone and follow the prompt inside it. You are the client under test.That is the whole setup. From there the assistant clones the repo, runs the smoke test, registers the probe as a local MCP server, runs the probe interactions, inspects the trace, and writes the result file. It comes back to you only for the things it genuinely cannot do itself: restarting the client so it picks up the MCP config, invoking anything the client exposes only as a user action, and approving the push or pull request.
This assumes a client that can run shell commands and read local files, such as Claude Code, Codex CLI, OpenCode or Cursor. If yours cannot, use Option B.
Option B: Step By Step
The same test, spelled out. Use this if your client cannot clone on its own, or if you want to see what Option A will do before you run it.
Clone this repository.
git clone https://github.com/kascada/mcp-client-compat-probe.git cd mcp-client-compat-probeHTTPS is recommended for most testers because it works without a configured SSH key. If you already use GitHub over SSH, this is equivalent:
git clone git@github.com:kascada/mcp-client-compat-probe.git cd mcp-client-compat-probeOpen the cloned directory in the MCP-capable assistant/client you want to test.
Ask the assistant to run
PROMPT.md, for example:Run PROMPT.md. If the assistant cannot read local files, paste the full content ofPROMPT.mdinstead.Follow only the explicit prompts for client restart, MCP setup confirmation, and push/PR approval.
The assistant should handle the rest:
run
npm run smokehelp configure the local
stdioMCP server if neededrun the probe interactions
inspect the trace file
write
results/<client>-<username>-<date>.mdstage and commit only that result file
Do not commit full trace files by default. Result files should include only small redacted excerpts.
Related MCP server: jakegaylor-com-mcp-server
Contributing A Result
This repository is public, which means anyone can read and clone it, but not push to it. Cloning does not create a fork and grants no write access, so contributing a result goes through a pull request from your own fork. The assistant can do this for you; the manual equivalent is:
gh repo fork --remote # your own fork, no permissions needed here
git switch -c probe-result-<client>-<username>
git add results/<client>-<username>-<date>.md # only the result file
git commit -m "Add <client> probe result <username> <date>"
git push -u origin probe-result-<client>-<username> # pushes to your fork
gh pr create --repo kascada/mcp-client-compat-probeUse your GitHub account name as <username>, so the result is attributable in the shared collection.
If you cannot or do not want to open a pull request, both of these are fine too:
Open an issue and attach the result file.
Send the result file to the repository author directly, together with the client version, the operating system, and your MCP config with secrets removed.
Files
mcp-probe/
README.md # quickstart and feature overview
CLIENT-MATRIX.md # informal client support matrix
PROMPT.md # assistant prompt for running and recording tests
TESTPLAN.md # repeatable client test plan
probe-core.mjs # JSON-RPC handlers and probe tools
stdio-server.mjs # local stdio transport
opencode.json # isolated OpenCode test config
package.json # npm scripts, no dependencies
results/ # contributed client observations
scripts/smoke-stdio.mjs # direct stdio smoke testProbe Coverage
Implemented MCP methods:
server/discoverlegacy
initializefallback responsetools/listtools/callresources/listresources/readresources/templates/listprompts/listprompts/getstub
subscriptions/listen
Tools:
echo_meta: returns received arguments,_meta, client capabilities, and transport observations.structured_result: returns text plusstructuredContentmatching anoutputSchema.create_handle: creates an explicit state handle.use_handle: uses a handle fromcreate_handle.needs_form_input: returnsresultType: "input_required"until retried withinputResponses.tool_error: returns a tool execution error viaisError: true.resource_link_result: returns aresource_linkcontent item.search: ChatGPT-compatible search stub.fetch: ChatGPT-compatible fetch stub.
Smoke Test
Run from this directory:
npm run smokeOr without npm:
node scripts/smoke-stdio.mjsThe smoke test writes its trace to:
/tmp/mcp-probe-smoke.ndjsonTrace Log
The server never writes diagnostics to stdout, because stdout must contain only MCP JSON-RPC messages. Diagnostics go to stderr and the trace file.
Default trace path:
/tmp/mcp-probe.ndjsonOpenCode trace path from opencode.json:
/tmp/mcp-probe-opencode.ndjsonEach line is JSON with:
ts: timestamppid: server process IDdirection:inoroutpayload: JSON-RPC payload
Test With OpenCode
This directory contains an isolated opencode.json:
{
"$schema": "https://opencode.ai/config.json",
"mcp": {
"probe": {
"type": "local",
"command": ["node", "stdio-server.mjs"],
"cwd": ".",
"enabled": true,
"timeout": 10000,
"environment": {
"MCP_PROBE_TRACE": "/tmp/mcp-probe-opencode.ndjson"
}
}
}
}Start OpenCode from this directory so it loads the local config:
opencodeThen ask:
Nutze das probe echo_meta Tool und zeige mir, welche MCP-Metadaten du gesendet hast.Additional useful prompts:
Nutze probe structured_result mit label opencode.Erzeuge mit probe create_handle ein Handle fuer confluence und nutze es danach mit probe use_handle fuer die Query release notes.Teste probe needs_form_input fuer topic OpenCode Elicitation.Nutze probe search fuer query probe und danach probe fetch fuer das erste Ergebnis.Interpret the trace:
server/discoverpresent: modern MCP discovery probe is used.initializepresent: legacy handshake path is used._meta.io.modelcontextprotocol/protocolVersionpresent: per-request protocol version is sent._meta.io.modelcontextprotocol/clientCapabilities.elicitationpresent: client declares elicitation support.resources/listorprompts/listpresent: client actively queries non-tool primitives.Retry after
input_required: MRTR/Elicitation flow is handled.
OpenCode reads config at startup. Restart OpenCode after changing opencode.json or server files.
Test With Codex CLI Or ChatGPT Desktop
The same local stdio server can be used by Codex CLI, ChatGPT Desktop app, and Codex IDE extension because they support local MCP servers.
Example Codex CLI registration from this directory:
codex mcp add probe --env MCP_PROBE_TRACE=/tmp/mcp-probe-codex.ndjson -- node stdio-server.mjsThen use /mcp in Codex to inspect active servers and ask for the same probe tools as above.
For ChatGPT Desktop app, add a new MCP server in Settings with:
Name:
probeType:
STDIOCommand:
nodeArgs: absolute path to
stdio-server.mjsEnvironment:
MCP_PROBE_TRACE=/tmp/mcp-probe-chatgpt-desktop.ndjson
ChatGPT Web And OpenAI API Path
ChatGPT Web cannot directly start a local stdio server or read local Codex/OpenCode configuration. For ChatGPT Web or OpenAI API testing, add a remote HTTP adapter later.
The current design keeps that path open:
probe-core.mjshas no stdio-specific behavior.stdio-server.mjsonly adapts newline-delimited JSON-RPC tohandleJsonRpc.A future
http-server.mjscan call the samehandleJsonRpcand pass HTTP headers in the transport object.The existing
searchandfetchtools already follow the simple ChatGPT-compatible shape withstructuredContentand URL-backed results.
HTTP-specific checks to add later:
MCP-Protocol-Version,Mcp-Method,Mcp-Namestatic/Bearer headers
OAuth behavior
x-mcp-headerfrom tool parametersStreamable HTTP response behavior
Available Tools
9 toolscreate_handleCreate HandleA
Creates an explicit short-lived probe handle to test stateless multi-call tool design.
| Name | Required | Description | Default |
|---|---|---|---|
| target | Yes | Target system or scenario for the handle. |
Output Schema
| Name | Required | Description |
|---|---|---|
| handle | Yes | |
| target | Yes | |
| expiresInSeconds | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral disclosure. It mentions the handle is 'short-lived' and 'explicit,' but does not explain what the handle is for, what it returns, any side effects, or lifecycle details. For a creation tool, this is insufficient.
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?
The description is a single sentence, front-loaded with the action, and contains no unnecessary words. It is appropriately concise.
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?
The tool is simple (1 parameter) and has an output schema, so the description does not need to explain return values. However, it lacks context about how the handle is used, its lifecycle, and its relationship to sibling tools like use_handle. This incomplete context could confuse agents.
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?
The input schema has 100% description coverage for the 'target' parameter, so the baseline is 3. The tool description adds no additional parameter-level context beyond restating the purpose.
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 clearly states the verb 'creates' and the resource 'explicit short-lived probe handle,' and it adds the specific purpose 'to test stateless multi-call tool design.' This distinguishes it from sibling tools like use_handle, which presumably consumes the handle.
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?
The description implies usage for testing stateless multi-call tool design but does not explicitly state when to use this tool versus alternatives like use_handle. No exclusions or when-not-to-use guidance is provided.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
echo_metaEcho MetadataA
Returns the received arguments and MCP request metadata. Use this first to inspect protocolVersion, clientInfo, and clientCapabilities.
| Name | Required | Description | Default |
|---|---|---|---|
| message | No | Any message to echo back. |
Output Schema
| Name | Required | Description |
|---|---|---|
| meta | Yes | |
| observed | Yes | |
| arguments | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden. It transparently states that the tool returns the received arguments and MCP metadata, and specifically calls out the metadata fields. This is a read-only behavior implied by 'Returns,' and it discloses what the agent can expect without needing to infer hidden side effects.
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?
The description is exactly two sentences. The first sentence states the core function, and the second provides usage guidance. Every word earns its place, with no filler or repetition. It is front-loaded with the primary purpose and immediately actionable.
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?
This is a simple tool with one optional parameter and an output schema present. The description fully covers its purpose and usage context. Since the output schema exists, the description does not need to explain return values. For the tool's complexity, the description is complete and well-rounded.
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?
The input schema fully documents the only parameter 'message' with a description ('Any message to echo back'), so schema coverage is 100%. The description does not add any additional parameter-specific meaning beyond what the schema provides, but it does mention 'received arguments' which encompasses the parameter. This meets the baseline of 3.
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 clearly states the tool 'Returns the received arguments and MCP request metadata,' which is a specific verb+resource combination. It distinguishes itself from siblings by explicitly mentioning metadata fields (protocolVersion, clientInfo, clientCapabilities) and the directive to 'Use this first,' making its diagnostic role clear.
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?
The description gives explicit usage context: 'Use this first to inspect protocolVersion, clientInfo, and clientCapabilities.' This tells the agent when to invoke the tool, though it does not explicitly name alternatives or exclusions. The clear 'use this first' directive provides adequate guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
fetchFetch Probe DocumentARead-only
ChatGPT-compatible read-only fetch stub. Retrieves full text for an ID returned by search.
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | Document ID returned by search. |
Output Schema
| Name | Required | Description |
|---|---|---|
| id | Yes | |
| url | Yes | |
| text | Yes | |
| title | Yes | |
| metadata | No |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnlyHint annotation, the description adds that this is a 'ChatGPT-compatible' and a 'stub,' suggesting a simulated or compatibility-oriented behavior, and that it returns 'full text' for the ID. This provides useful context not present in annotations, with no contradictions.
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?
The description is two short sentences with no filler. The first provides contextual framing ('stub'), the second the core functionality. Every word contributes meaning.
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 simple one-parameter fetch operation with an output schema and clear read-only annotation, the description sufficiently covers purpose, input requirement, and relationship to search. The 'stub' characterization adds a behavioral hint without needing further detail.
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?
The schema already provides 100% parameter coverage with 'Document ID returned by search.' The tool description echoes the same requirement without adding new semantic details, so it stays at the baseline for high schema coverage.
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 clearly states 'Retrieves full text for an ID returned by search,' specifying the verb (retrieves), resource (full text), and the relationship to the search tool. This distinguishes it from siblings like search (which finds IDs) and handle tools.
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?
The description explicitly ties usage to search by requiring an ID returned by search, implying the correct invocation sequence. It does not explicitly name alternatives or exclusion conditions, so it doesn't reach a 5.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
needs_form_inputNeeds Form InputA
Returns resultType input_required until the client retries with inputResponses. This tests MRTR and elicitation form mode.
| Name | Required | Description | Default |
|---|---|---|---|
| topic | Yes | Topic for the requested follow-up input. |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses the key behavioral trait: the tool repeatedly returns input_required until the client sends inputResponses. However, it doesn't specify what happens after the retry or any side effects, but for a simple test tool this is adequate.
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 sentences, front-loaded with the return behavior and testing purpose. No wasted words.
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 simple tool with one parameter and no output schema, the description covers the core behavior and purpose. It might benefit from stating the expected response after inputResponses, but the description is sufficient for an agent to understand invocation context.
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 clear description of 'topic'. The main description doesn't add significant new meaning beyond the schema; it reinforces the context of follow-up input but doesn't explain format or constraints. Baseline 3 applies given high schema coverage.
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 explicitly states the tool's behavior: it returns resultType input_required until retried with inputResponses. It also states its testing purpose (MRTR and elicitation form mode), clearly distinguishing it from siblings like echo_meta or structured_result.
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?
The description identifies a clear use case: testing MRTR and elicitation form mode. It doesn't explicitly mention when not to use it or alternatives, but the testing context is specific enough for an agent to select it appropriately.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
resource_link_resultResource Link ResultC
Returns a resource_link content item pointing at a probe resource.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It only states the return type and points at a probe resource, but gives no information about side effects, error behavior, permissions, or whether the operation is read-only. This is minimal transparency.
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?
The description is a single sentence with no filler. It is appropriately concise and front-loaded, stating the core behavior immediately.
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?
With no output schema and no annotations, the description is too sparse. It does not explain what a resource_link content item is, what a probe resource is, or how to handle the result. This leaves significant gaps for an agent selecting among sibling tools.
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?
The tool has zero parameters, so the description has no need to explain parameter syntax or semantics. The baseline for zero parameters is 4, and the description does not miss anything here.
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 clearly states the tool returns a resource_link content item, which is specific and differentiates it somewhat from generic tools. However, it does not clarify what a 'probe resource' is or how this differs from sibling result tools like structured_result or echo_meta.
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?
There is no guidance on when to use this tool versus alternatives. The description lacks any mention of prerequisites, exclusions, or sibling tools, leaving the agent without a basis for selection.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
searchSearch Probe DocumentsARead-only
ChatGPT-compatible read-only search stub. Returns result IDs, titles, and URLs. Use fetch to retrieve full text.
| Name | Required | Description | Default |
|---|---|---|---|
| query | Yes | Search query. |
Output Schema
| Name | Required | Description |
|---|---|---|
| results | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The readOnlyHint annotation already covers safety, and the description adds context by stating it is a 'stub' and returns specific fields (IDs, titles, URLs). This provides behavioral insight beyond the annotation, though it does not elaborate on limitations like pagination or result counts.
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?
The description is a single concise sentence that states purpose, output, and usage guidance without any redundancy. It is front-loaded and immediately clear.
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?
Given the simple one-parameter search tool, the description covers its return values and relationship to fetch. The presence of an output schema and annotations reduces the burden, and the description fills the essential gaps.
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?
The schema has 100% coverage for the single 'query' parameter with a basic description. The tool description does not add any additional semantics beyond the schema, so baseline 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 clearly states that the tool performs a search, returns result IDs, titles, and URLs, and is specifically for probe documents. It distinguishes from the sibling tool 'fetch' which retrieves full text, making the purpose unambiguous.
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 'Use fetch to retrieve full text,' providing a clear alternative and when to use another tool. It also labels the tool as read-only, suggesting it is for search queries only, not for retrieval or modification.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
structured_resultStructured ResultB
Returns both text content and structuredContent conforming to outputSchema.
| Name | Required | Description | Default |
|---|---|---|---|
| label | No | Optional label for the generated result. |
Output Schema
| Name | Required | Description |
|---|---|---|
| label | Yes | |
| answer | Yes | |
| nested | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description must carry the full burden of disclosing behavior. It does state the core return behavior (both text and structuredContent), which is useful, but it does not address the role of the label parameter, edge cases, or any limitations. This is minimal but not 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?
The description is one sentence that front-loads the primary action and includes no filler or redundant information. Every word contributes to understanding the tool's function, making it highly concise and well-structured.
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?
The tool is simple: one optional parameter, no required fields, and an output schema. The description states the core return behavior, and the output schema presumably covers the structure of structuredContent. However, it does not mention the intended use case or how the label parameter influences the result, leaving a small but noticeable gap. Given the simplicity, it is mostly complete.
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?
The input schema has 100% coverage for the single optional 'label' parameter, described as 'Optional label for the generated result.' The description adds no further semantic detail about how the label affects the output, so it remains at the baseline for high schema coverage without adding extra value.
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 states the tool's primary function: returning both text content and structuredContent conforming to outputSchema. This clearly identifies what the tool does, though it does not explicitly differentiate it from sibling tools like resource_link_result. The verb 'Returns' and the specific resource make the purpose clear.
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?
There is no guidance on when to use this tool versus alternatives. The description only states what it does, without mentioning any context, prerequisites, or exclusions. Sibling tools are listed but not referenced, so the description fails to help the agent decide when to invoke this tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
tool_errorTool ErrorA
Always returns a tool execution error via isError true, not a JSON-RPC protocol error.
| Name | Required | Description | Default |
|---|---|---|---|
No parameters | |||
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full disclosure responsibility. It clearly states the tool always errors with isError true and clarifies that it is not a protocol-level error, providing useful context. It does not detail the error message content, but the key behavioral trait is fully disclosed.
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?
The description is a single sentence with the core behavior front-loaded ('Always returns a tool execution error'). It is concise and contains no unnecessary words or filler.
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-parameter, no-output-schema tool, the description is fully complete. It precisely specifies what the tool does without needing to explain parameters or return values. The purpose is fully captured.
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?
The tool has zero parameters, so the empty schema is fully covered. The description adds no parameter semantics because none are needed. The baseline for 0 params is 4.
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 clearly states the tool always returns a tool execution error via isError true, and explicitly distinguishes this from a JSON-RPC protocol error. This specific verb and resource make the tool's purpose unambiguous and differentiate it from siblings like structured_result or echo_meta.
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?
The description only states what the tool does, not when or why to use it. It does not reference any testing scenarios or contrast with alternative tools. There is no when-to-use or when-not-to-use guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
use_handleUse HandleC
Uses a handle returned by create_handle. Unknown handles return a tool execution error.
| Name | Required | Description | Default |
|---|---|---|---|
| query | Yes | Probe query to associate with the handle. | |
| handle | Yes | Handle returned by create_handle. |
Output Schema
| Name | Required | Description |
|---|---|---|
| query | Yes | |
| handle | Yes | |
| target | Yes | |
| callCount | Yes |
TDQS
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses one behavioral trait: unknown handles return a tool execution error. But it does not describe success behavior, side effects, or whether the operation is read-only or mutating. This is minimal transparency beyond the error condition.
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?
The description is a single, compact sentence that states the essential dependency on create_handle and the error behavior for unknown handles. It is appropriately sized and front-loaded, with no wasted words.
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?
Despite having an output schema and two well-documented parameters, the description fails to convey the tool's actual operation or purpose. It does not explain what 'uses a handle' accomplishes, making the tool's functionality incomplete for an agent trying to select and invoke it correctly. The error condition is noted, but the success path and overall behavior are absent.
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 description coverage is 100%, so the baseline is 3. The description reinforces the handle parameter's origin ('returned by create_handle') but adds no additional meaning to 'query' beyond the schema's 'Probe query.' It does not compensate for or enhance the parameter understanding beyond what the schema already provides.
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 states it 'Uses a handle returned by create_handle,' which identifies the tool as the counterpart to create_handle and distinguishes it by its dependency on a prior handle. However, the verb 'uses' is vague—it does not specify what action is performed with the handle or what output is produced, leaving the core purpose unclear.
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?
The description implies that the tool should be used after create_handle, since it requires a handle returned by that tool. It also warns that unknown handles error, which guides the user to provide a valid handle. However, it does not state when to use this tool instead of other siblings (e.g., search, fetch) or specify exclusions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
TDQS
Each tool targets a distinct MCP feature: metadata inspection, structured output, handle-based state, MRTR input, error simulation, resource links, and search/fetch stubs. There is no overlap between their purposes.
Names are a mix of verb_noun (echo_meta, create_handle), standalone verbs (search, fetch), and nouns (structured_result, tool_error). While all are snake_case, the varying forms make the naming pattern less predictable than a uniform verb_noun convention.
9 tools is a well-scoped set for a compatibility probe, covering the key MCP client interaction patterns without redundancy or bloat.
The tool surface covers essential probe scenarios: metadata, structured content, handles, MRTR, errors, resource links, and search/fetch. Minor gaps exist (e.g., no explicit tool for protocol-level logging or sampling), but the core compatibility checks are well represented.
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