@descryy/mcp

Descry's MCP server. It reads a repository's source into a graph of code, routes, tables and tests, and lets a coding agent ask that graph what a change reaches, what is tested, and what breaks when the app runs.

It reports a few findings it can back with evidence, and an explicit list of what it could not check. Something it could not read is reported as "not analysable", never as clean.

Everything runs on your machine. The graph lives in the repository's .descry/ folder.

Requirements

• Node.js 22.5 or newer (the graph uses Node's built-in SQLite).
• A git repository with at least one commit. Every node in the graph is stamped with the commit it was read at, so a folder that is not a repository, or a repository with no commits, cannot be built.
• Linux for sandboxed runs. The observe and generate_test tools run your code inside a sandbox: bubblewrap by default, with the network denied, or Docker with sandboxBackend: "container". If neither works they refuse to start instead of running unconstrained. Descry's own tests run on Linux; macOS and Windows have not been verified.
• Chromium, only for the browser tools. npx -y @descryy/cli setup installs it. Without it those tools refuse and say why.

Quickstart

1. In the repository, write its configuration:

   npx -y @descryy/cli init
   

   This detects the language adapters that recognise the repository, writes them to .descry/config.json, and prints the next two steps with this server's exact version filled in.

2. Register the server with your agent. For Claude Code:

   claude mcp add descry --scope local -- npx -y @descryy/mcp@<version> "$(pwd)"
   

   Use the version init printed. For any other MCP client, the server is a stdio command: npx with the arguments -y, @descryy/mcp@<version>, and the absolute path of the repository.

3. In the agent, call the workspace tool with verb analyze (or run npx -y @descryy/cli analyze). That builds the graph. Every other tool then answers from it, and most will build it themselves on first use.

A repository with no .descry/config.json, or one with no sources, connects but cannot build. The first reply from any tool says so on its first line and names the fix: run the init command above, or call workspace with verb setup.

Commit .descry/config.json and .descry/.gitignore. Everything else in .descry/ is this machine's and is ignored by git.

Tools

Eighteen tools, and a nineteenth, descry_confirm, that only a client known to ask the person before every call to it is shown. The class says what a call can do: read only reads, stateful-read may write Descry's own derived files (the graph, inventories) and is safe to repeat, and action does something that is not a plain read (runs repository code, drives a browser, or writes a configuration or store). A tool's class is that of its strictest verb. tools/list also carries verbClasses for a tool whose verbs differ, and every reply's class is the class of the verb that was called, so questions with nothing to record is read, an answer is stateful-read and workspace with verb analyze is stateful-read. A verb that has nothing to confirm runs on one call, whatever its tool's class; each tool's description says which verbs ask first.

Required arguments are stated per verb. The schema keeps only verb as required, because some hosts reject conditional schemas, so each argument's description says which verbs need it and the schema carries the same rules in an x-requiredByVerb keyword. A call that leaves one out is refused before anything runs, naming it. A limit whose default differs by verb lists the defaults one by one, and x-defaultsByVerb carries them as numbers.

Long calls report progress when the client sent a progress token: a message every few seconds naming the call and how long it has run. Cancelling a call stops its progress and sends no answer for it, though a tool that does not read its cancellation signal may keep working until it finishes.

Confirming actions

A verb that runs code, writes into a repository or drives a browser with write safety does nothing on its first call. It returns a description of exactly what it will do, a confirmToken, and (where a queue is available) an approval id. Calling the same tool again with that token runs it, but only after a person has approved that exact description. A token is single-use, bound to the arguments of the first call (a changed argument on the second call is discarded and named in the reply), and expires after 15 minutes. A token the calling agent presents on its own authority is refused, and the refusal lists the ways to get it approved. It stays valid after a refusal, so the approval can arrive later.

A token is approved by any one of these:

1. descry_confirm, in Claude Code. The agent calls descry_confirm with token and with summary set to the sentence the first call returned, character for character. The tool is marked anthropic/requiresUserInteraction, so Claude Code shows its own permission prompt on every call, in every permission mode including auto, and an allow rule cannot skip it. The person reads the sentence in that prompt. Then the agent calls the verb again with the same arguments and the same confirmToken. A summary that is not the stored sentence is refused and changes nothing; a denied prompt leaves the token pending. In dontAsk mode, and in a headless run with no one to answer, Claude Code denies the call, and the other routes apply. The tool is listed, and honoured, only when the client names itself as a Claude Code version that supports the flag; for any other client it does not exist and the reply names the other routes. Each outcome is recorded in ~/.descry/approvals-audit.jsonl (a short token reference, never the token).
2. MCP elicitation. If the client declares it, the second call asks the person directly, showing the exact text. It runs only if they approve, and a decline by a person is final for that token. A decline that came back faster than anyone could read it is reported as unattended, and the token stays pending for another route.
3. descry approvals, at a terminal. The first call of a gated verb queues an approval under ~/.descry/approvals (15 minutes, at most 50, never the arguments themselves). descry approvals list shows what is waiting, descry approvals approve <id> shows the sentence and has the person type the id back, and descry approvals deny <id> refuses. The agent's next call with its token then runs once. This needs no client support, so it works in the VS Code extension, in auto mode and in headless runs.
4. A standing approval, made at a terminal. descry approve makes a file under ~/.descry/grants, private to the user, bound to this repository, with a time limit and no --yes: browser --origin <address> for read-only sessions on exact origins (up to 7 days), browser --write --origin <loopback address> for write-level sessions on localhost, 127.0.0.1 or [::1] only, tests --command <command> for one test command typed exactly, sandbox for qa validate_tests and generate_test verify in this repository, and store for writes to Descry's own store. The last three and the write kind last at most 24 hours. descry approve --list shows them and --revoke <id> removes one. A call a grant covers says which grant approved it.
5. The command-line twin of the verb, for a person or a pipeline: descry browse, descry observe tests, descry qa validate-tests, descry scenario record, descry trust, descry init, descry setup, descry analyze. Each prints the same consent text the server would, asks at the terminal, and with no terminal refuses unless --yes is given. The prompt reads from the controlling terminal, discards anything pasted before it appeared, and takes only what is typed after it. Run each command alone and wait for its prompt.

DESCRY_REQUIRE_HUMAN_CONFIRMATION is on unless set to 0. With it on, as it is by default, no client can confirm for itself. Set it to 0 in the server's environment only for a setup where the calling agent is meant to confirm its own actions (a script you wrote and trust).

Do not redeem tokens through a side client, a script or a shell command, and do not add a hook that approves whatever Descry asks. The value of the step is that a person saw the sentence.

Three confirmations are worth knowing before you meet them.

workspace with verb trust_sources. .descry/config.json lists adapter modules, and loading one runs its code with options the repository chose. Because a repository can change that file, a source is not loaded until this machine has confirmed it. The first call lists exactly which module, export and options would load; the second records the confirmation outside the repository, in ~/.descry/confirmed-sources.json. A change to the module, export or options asks again. init and setup confirm the adapters they write themselves. To confirm one repository without a prompt, run descry trust (npx -y @descryy/cli trust) in it. To trust every repository this server opens, set DESCRY_TRUST_CONFIGURED_SOURCES=1 in the server's environment; that covers every repository, not just one. While adapters are untrusted, every graph read leads its headline with "Source not read" and reports its freshness as unread.

Replaying a saved scenario. browser with verb run_scenario replays a committed file from descry/scenarios/. A scenario this machine has not approved at its current content gets the two-call confirmation first. The first call names the file, its content hash, the origins it visits and the secret references it types, and replays nothing. Approval is stored in ~/.descry/approved-scenarios.json; editing the file asks again.

Running your code. observe and generate_test start the application or its tests, in the sandbox described above. qa with verb validate_tests also runs your tests, against deliberate changes to the code they cover, and takes the same two calls. The first call says what will be started.

Running an evaluation

An unattended run (a benchmark, a CI job, an agent harness) has no person to answer the consent prompts, so set it up before the first call:

1. Run npx -y @descryy/cli init --yes in the repository first. It writes .descry/config.json and confirms the adapters it detected, so the first tool call reads source instead of asking for setup.
2. Build the graph once with npx -y @descryy/cli analyze, or call workspace with verb analyze.
3. For the verbs that run code, write files or drive a browser, choose one route from "Confirming actions" above. For a harness you wrote and trust, start the server with DESCRY_REQUIRE_HUMAN_CONFIRMATION=0 so the agent's second call with its confirmToken runs. Add DESCRY_TRUST_CONFIGURED_SOURCES=1 if the repository's .descry/config.json names adapters this machine has not confirmed. Both settings apply to every repository the server opens; keep them out of an everyday setup.
4. Read each reply's category and its "What this answer does not cover" list. A refusal or a partial result is reported as one, and scoring it as a wrong answer measures the wrong thing.

Reading a result

Every answer states how much it rests on. A finding carries one of these categories:

• confirmed-observed: confirmed, and backed by evidence from a real run of the application.
• confirmed-code-only: confirmed from the code alone, on direct evidence of the mechanism from two or more independent kinds. Nothing was observed running.
• strongly supported: the evidence is strong but short of confirmed.
• unconfirmed: a prediction. It is never reported as fact.
• not analysable: Descry could not read this part, here. That is different from "found nothing".
• unsupported: Descry does not do this at all.

Each reply also lists what it does not cover, including a stale graph, a language with no adapter, and references the graph could not resolve. Test coverage is a separate axis, reported as verification status.

Troubleshooting

npx -y @descryy/cli doctor

checks the Node version and built-in SQLite, that one copy of the engine is installed, that the CLI and the server beside it are the versions released together, npx's cache for a half-extracted package, the standing approvals and the approvals waiting for you, and, in a repository, its git state, config, adapters, whether this machine has confirmed them, and the graph. Each finding names its fix. --fix removes only the broken Descry entries from npx's cache.

Common first-run messages:

• "has no .descry/config.json yet" or "has no sources": run npx -y @descryy/cli init, or call workspace with verb setup.
• "not confirmed on this machine" or "no source was read": see the entry below.
• "is not a git repository" or "has no commits yet": run git init and make a first commit.
• "descry-mcp: not found" or ENOTEMPTY from npx: run doctor --fix.

Analyze says no source was read / adapter not confirmed

The graph then holds only git history, no code. Fix it in this order:

1. Run npx -y @descryy/cli init --yes in the repository, which records this machine's confirmation of the adapters it writes. Or run descry trust [--yes] [path], which confirms a repository's configured adapters on this machine, per repository. descry analyze then builds the graph from the command line.
2. If the config already listed adapters, call workspace with verb trust_sources from the agent and approve the prompt it raises. A client that cannot show an approval prompt cannot complete this step; use step 1.
3. Call workspace with verb analyze again (or run descry analyze).

Do not set DESCRY_TRUST_CONFIGURED_SOURCES=1 in a global server entry. It trusts every repository the server opens, and a repository can change its adapter list by editing a committed file. If you need it, set it for one trusted repository, in that repository's own server entry.

Claude Code permissions and auto mode

Claude Code decides each tool call before Descry sees it, by an allow rule, an ask rule or, in auto mode, a classifier; Descry's own approval comes after. An allow rule answers only the first. Rules are named mcp__<server-name>__<tool>, where <server-name> is the name given to claude mcp add. In .claude/settings.local.json:

{
  "permissions": {
    "allow": [
      "mcp__descry__code_context",
      "mcp__descry__git_context",
      "mcp__descry__disclosure",
      "mcp__descry__check",
      "mcp__descry__reach",
      "mcp__descry__similar_incidents",
      "mcp__descry__draw_conclusion"
    ]
  }
}

Those seven only read. The tools with write or run verbs (workspace, change_scope, qa, generate_test, observe, browser, browser_read, prove_reach, questions, mark_incident) can be allowed by rule too, because their first call changes nothing and the person is asked at descry_confirm, which an allow rule cannot skip. Allowing them also lets Claude Code's classifier stop denying a harmless first call. Allow mcp__descry__descry_confirm and Claude Code still asks the person on every call.

If a gated call is declined within a fraction of a second, something other than a person declined it. Look for an Elicitation hook (grep -n Elicitation ~/.claude/settings.json .claude/settings.local.json), for --permission-prompts none, and for a non-interactive launch. An Elicitation hook that blanket-accepts defeats the step; if you write one, accept only a message that names a loopback origin and a read-only or sandboxed verb, and exit without a decision otherwise. autoMode settings in ~/.claude/settings.json can describe the setup in prose (a .descry/ store and a loopback dev app are expected); they cannot name a tool, and are read only from user or managed settings.

When Claude Code starts a new session onto a newer Descry, its own tool list can still show the old verbs. Descry announces notifications/tools/list_changed once on the first connection after its tool surface changes, which makes clients that honour it re-list; for one that keeps its own cache, restart the session or reconnect the server.

Known limits

• Playwright and other end-to-end tests are linked to code only through executed coverage (observe verb tests). A static link from a test's page.goto is limited to exact literal paths, so until coverage has run, such a suite shows as registered but not covering anything.
• The reliability class of a change-scope answer is the minimum over the edges that answer touched. A broad diff can be class C because of a handful of R0 edges.
• A frontend-only repository has no API routes in its graph, so check verb contracts is not analysable until the backend repository is linked with workspace verb link.

Privacy

Descry has no hosted component, and this server calls no Descry service. The graph, evidence, findings and answers you record are files in .descry/ in your repository, and only config.json is meant to be committed. Confirmations are kept in ~/.descry/ on this machine, and stored browser credentials are encrypted there. The browser and runtime tools talk only to the application address you give them.

License

MIT