🔍 LSP Integration

Query language servers for diagnostics, navigation, symbols, renames, code actions, capabilities, and raw requests.

Source

• Entry: packages/coding-agent/src/lsp/index.ts
• Model-facing prompt: packages/coding-agent/src/prompts/tools/lsp.md
• Key collaborators:
  • packages/coding-agent/src/lsp/client.ts — client process lifecycle and JSON-RPC
  • packages/coding-agent/src/lsp/config.ts — config loading, auto-detect, server selection
  • packages/coding-agent/src/lsp/lspmux.ts — optional lspmux command wrapping
  • packages/coding-agent/src/lsp/edits.ts — apply WorkspaceEdit and text edits
  • packages/coding-agent/src/lsp/utils.ts — URI conversion, symbol resolution, formatting, glob expansion
  • packages/coding-agent/src/lsp/types.ts — tool schema and protocol types
  • packages/coding-agent/src/lsp/clients/index.ts — custom linter client cache/factory
  • packages/coding-agent/src/lsp/clients/lsp-linter-client.ts — LSP-backed linter adapter
  • packages/coding-agent/src/lsp/clients/biome-client.ts — Biome CLI diagnostics/formatting adapter
  • packages/coding-agent/src/lsp/clients/swiftlint-client.ts — SwiftLint CLI diagnostics adapter
  • packages/coding-agent/src/tools/index.ts — tool registration and lsp.enabled gating
  • packages/coding-agent/src/tools/tool-timeouts.ts — timeout defaults and clamping
  • packages/coding-agent/src/lsp/defaults.json — built-in server definitions for auto-detect

Inputs

Field	Type	Required	Description
action	string enum	Yes	One of diagnostics, definition, references, hover, symbols, rename, rename_file, code_actions, type_definition, implementation, status, reload, capabilities, request.
file	string	No	File path; for diagnostics also a glob; for workspace forms use "*"; for rename_file this is the source path.
line	number	No	1-indexed line number for position-based actions. Defaults to 1 on the single-file action path.
symbol	string	No	Substring used to resolve the column on line. Supports name#N occurrence selectors; N is 1-indexed and defaults to 1. Required when line is given for definition/references/rename against project-aware servers.
query	string	No	Workspace symbol query, code-action selector/filter, or LSP method name for action=request.
new_name	string	No	Required for rename and rename_file.
apply	boolean	No	For rename/rename_file, apply unless explicitly false. For code_actions, list unless explicitly true.
timeout	number	No	Seconds, clamped by clampTimeout("lsp", ...) to 5..60, default 20.
payload	string	No	JSON string for action=request; overrides auto-built params.

Outputs

• Single-shot AgentToolResult.
• content is always one text block: [{ type: "text", text: string }].
• details is LspToolDetails: action, success, optional serverName, optional original request.
• No streaming updates.
• No artifact URIs or background jobs.
• Many validation failures are returned as ordinary text results with details.success: false; aborts throw ToolAbortError instead.

Flow

1. packages/coding-agent/src/tools/index.ts registers lsp: LspTool.createIf; session creation also gates it behind session.enableLsp !== false and settings.get("lsp.enabled").
2. LspTool.execute() in packages/coding-agent/src/lsp/index.ts clamps timeout with clampTimeout("lsp", ...), builds an AbortSignal.timeout(...), and combines it with the caller signal.
3. getConfig() loads and caches LspConfig per cwd, applies idle-timeout config via setIdleTimeout(), and reuses the cached config on later calls.
4. Config loading in packages/coding-agent/src/lsp/config.ts merges defaults.json with JSON/YAML overrides from project, project config dirs, user config dirs, plugin roots, and home; if there are no overrides it auto-detects servers from root markers plus executable discovery.
5. Server routing uses getServersForFile() / getServerForFile() from config.ts: extension or basename match, then sort primary servers before linters. index.ts further filters custom linter clients out of navigation/refactor paths with getLspServersForFile() / getLspServerForFile().
6. getOrCreateClient() in client.ts creates one process per command:cwd, optionally wraps supported commands with lspmux, spawns the server, starts the background message reader, sends initialize, stores server capabilities, then sends initialized.
7. The message reader in client.ts parses LSP frames, resolves pending requests, caches publishDiagnostics, tracks $/progress tokens for project-load completion, answers workspace/configuration, and applies workspace/applyEdit requests through applyWorkspaceEdit().
8. File-scoped actions call ensureFileOpen() before requests. Column resolution uses resolveSymbolColumn() from utils.ts: read the target file, pick first non-whitespace when symbol is omitted, otherwise find the exact or case-insensitive match on the target line and honor #N occurrence selectors.
9. Actions dispatch in LspTool.execute() through dedicated branches: workspace-only branches (status, some diagnostics, workspace symbols, workspace reload, capabilities, request) run before the single-file switch; all other single-file actions share one client lookup and switch(action).
10. Requests go through sendRequest() in client.ts, which allocates an incrementing JSON-RPC id, installs abort and timeout handling, sends $/cancelRequest on abort, and rejects on timeout or process exit.
11. Actions that return edits either preview with formatWorkspaceEdit() or apply with applyWorkspaceEdit() from edits.ts; rename_file also performs the filesystem rename and then sends workspace/didRenameFiles.
12. Non-abort failures inside the single-file action block are converted to LSP error: ...; many precondition failures return explicit text without throwing.

Modes / Variants

Routing and workspace scope

• file: "*" is only special for diagnostics, symbols, and reload.
• status ignores file.
• capabilities with omitted file or "*" inspects all non-custom LSP servers; with a concrete file it scopes to matching non-custom servers.
• request with omitted file or "*" chooses the first available non-custom LSP server; with a concrete file it chooses that file’s primary non-linter server.
• rename_file sends workspace/willRenameFiles and workspace/didRenameFiles to every non-custom LSP server from getLspServers(config) whose fileTypes match the source, destination, or any enumerated rename pair — not just one file-scoped server.
• Diagnostics are the only tool action that queries both normal LSP servers and custom linter clients (BiomeClient, SwiftLintClient, or LspLinterClient).

diagnostics

Inputs

• Required: file, unless using workspace mode with file: "*".
• Optional: timeout.

Execution

• file: "*": runWorkspaceDiagnostics() detects project type from root markers and runs one subprocess command: Rust cargo check --message-format=short, TypeScript npx tsc --noEmit, Go go build ./..., Python pyright.
• Concrete file or glob: resolveDiagnosticTargets() treats non-globs as one target, otherwise expands a Bun.Glob up to MAX_GLOB_DIAGNOSTIC_TARGETS.
• Per file, every matching server runs: custom clients call lint(file); real LSP servers optionally wait for project load, capture diagnosticsVersion, refreshFile(), then waitForDiagnostics() for fresh publishDiagnostics (settles on the latest publish; exact-version match accepted immediately).
• Results are deduplicated by range+message and severity-sorted.

Output text

• Single target with no issues: OK.
• Single target with issues: <summary>:\n<grouped diagnostics>.
• Batch/glob target: one section per file, plus an initial truncation warning when the glob exceeds the file cap.
• Workspace mode: Workspace diagnostics (<detected description>):\n<command output>.

definition

Inputs

• Required: file.
• Optional: line, symbol, timeout.

Execution

• Sends textDocument/definition with { textDocument, position }.
• Accepts Location, Location[], LocationLink, or LocationLink[]; normalizeLocationResult() converts LocationLink to targetSelectionRange ?? targetRange.
• Requires symbol when line is given on project-aware servers (the first-non-whitespace-column fallback is disabled for this action).
• Waits for project load before the request.

Output text

• No definition found or Found N definition(s): followed by file:line:col and one context line above/below each location.

type_definition

Same as definition, but sends textDocument/typeDefinition and reports type definition(s).

implementation

Same as definition, but sends textDocument/implementation and reports implementation(s).

references

Inputs

• Required: file.
• Optional: line, symbol, timeout.

Execution

• Sends textDocument/references with includeDeclaration: true.
• Requires symbol when line is given on project-aware servers (the first-non-whitespace-column fallback is disabled for this action).
• For project-aware servers, retries up to REFERENCES_RETRY_COUNT times when the only hit is the queried declaration; between retries it waits for project load and sleeps REFERENCES_RETRY_DELAY_MS.
• First REFERENCE_CONTEXT_LIMIT references include surrounding context; the rest are location-only.

Output text

• No references found or Found N reference(s): with contextual entries first, then ... M additional reference(s) shown without context when truncated.

hover

Inputs

• Required: file.
• Optional: line, symbol, timeout.

Execution

• Sends textDocument/hover.
• extractHoverText() flattens strings, markup content, marked-string objects, or arrays into plain text.

Output text

• No hover information or the extracted hover text.

symbols

Inputs

• Workspace mode: file: "*" or omitted file on the early workspace branch, plus required query.
• Document mode: required file.
• Optional: timeout.

Execution

• Workspace mode sends workspace/symbol to every non-custom LSP server, post-filters matches with filterWorkspaceSymbols(), deduplicates with dedupeWorkspaceSymbols(), then truncates to WORKSPACE_SYMBOL_LIMIT.
• Document mode sends textDocument/documentSymbol to the primary server. If the first item has selectionRange, it formats hierarchical DocumentSymbols; otherwise it formats flat SymbolInformations.

Output text

• Workspace mode: Found N symbol(s) matching "query": plus formatted name @ file:line:col, with an omission line when over the limit.
• Document mode: Symbols in <file>: plus hierarchical or flat symbol lines.

rename

Inputs

• Required: file, new_name.
• Optional: line, symbol, apply, timeout.

Execution

• Requires symbol when line is given on project-aware servers, then waits for project load, sends textDocument/rename, receives a WorkspaceEdit.
• apply !== false applies edits immediately with applyWorkspaceEdit().
• apply === false renders a preview with formatWorkspaceEdit().

Output text

• Rename returned no edits, Applied rename: plus applied change lines, or Rename preview: plus summarized edits.

rename_file

Inputs

• Required: file source path, new_name destination path.
• Optional: apply, timeout.

Execution

• Resolves absolute source and destination, rejects identical paths, missing source, existing destination, empty rename set, or directories with more than MAX_RENAME_PAIRS files.
• enumerateRenamePairs() returns one {oldUri,newUri} pair for a file or walks every regular file in a directory tree.
• Sends workspace/willRenameFiles with { files: pairs } to every non-custom LSP server whose fileTypes match an affected path; collects returned WorkspaceEdits and server notes.
• Preview mode (apply === false) only formats those edits.
• Apply mode coalesces the returned text edits per URI (a project-aware server’s edits win on overlap; overlapping edits from other servers are discarded with a note), applies each URI once from a single snapshot, creates the destination parent directory and renames the source path on disk, sends textDocument/didClose for every renamed open file, deletes those openFiles entries, then sends workspace/didRenameFiles.

Output text

• Preview: Rename preview: <file-count label> → <dest> plus per-server edit summaries and optional server notes.
• Apply: Renamed <file-count label> → <dest> plus applied edit summaries, filesystem rename line, and optional server notes.

code_actions

Inputs

• Required: file.
• Optional: line, symbol, query, apply, timeout.

Execution

• Reads cached diagnostics for the open URI from client.diagnostics and sends textDocument/codeAction for a zero-width range at the resolved position.
• When apply !== true, query is passed as context.only: [query]; this is a server-side kind filter.
• When apply === true, query becomes a required client-side selector: either a zero-based numeric index or a case-insensitive substring of the action title.
• Applying a CodeAction uses applyCodeAction(): optionally codeAction/resolve, then applyWorkspaceEdit(edit), then optional workspace/executeCommand.
• Applying a bare Command only runs workspace/executeCommand.

Output text

• List mode: N code action(s): plus index: [kind] title lines.
• Apply mode success: Applied "title": plus Workspace edit: and/or Executed command(s): sections.
• Apply mode miss: No code action matches "query". Available actions:.
• Apply mode with no edit/command: Action "title" has no workspace edit or command to apply.

status

Inputs

• None.

Execution

• Reads configured servers from cached LspConfig and cross-references getActiveClients() so each server is labelled (configured, not started) or with its live client status.
• Calls detectLspmux() and appends status text when lspmux is installed.

Output text

• Language servers: <name (configured, not started) | name (<status>)> plus an explanatory note line, or No language servers configured for this project, optionally followed by lspmux: active (multiplexing enabled) or lspmux: installed but server not running.

reload

Inputs

• Workspace mode: file: "*" or omitted file.
• Single-file mode: required file.
• Optional: timeout.

Execution

• Workspace mode reloads every non-custom LSP server.
• Single-file mode reloads the primary server for that file.
• reloadServer() tries rust-analyzer/reloadWorkspace, then workspace/didChangeConfiguration with { settings: {} }; if neither works it kills the process so the next request cold-starts a new client.

Output text

• One line per server: Reloaded <server>, Restarted <server>, or Failed to reload <server>: ....

capabilities

Inputs

• Optional: file, timeout.

Execution

• With a concrete file, inspects matching non-custom servers for that file.
• With omitted file or "*", inspects every non-custom configured server.
• Starts servers as needed and dumps client.serverCapabilities ?? {} as pretty JSON.

Output text

• Per server: <server>: followed by indented capabilities: { ... }, or <server>: failed to start (...).

request

Inputs

• Required: query method name.
• Optional: file, line, symbol, payload, timeout.

Execution

• Chooses one non-custom server: file-scoped primary server, otherwise the first configured non-custom server.
• Param building precedence:
  1. If payload is present, parse JSON and use it verbatim.
  2. Else if file is concrete and line is present, build { textDocument: { uri }, position: { line: line - 1, character } } using resolveSymbolColumn().
  3. Else if file is concrete, build { textDocument: { uri } }.
  4. Else use {}.
• Opens the file first when file is concrete.

Output text

• Success: <server> ← <method>:\n<formatted result>, where non-string results are JSON.stringify(..., null, 2) and nullish values become null.
• Failure: LSP error from <server> on <method>: ... followed by params: <preview> echoing the request params (truncated to 400 chars).

Side Effects

• Filesystem
  • Reads config files, target files, and root markers.
  • rename and code_actions may edit/create/delete/rename files via applyWorkspaceEdit().
  • rename_file always renames the source path on disk in apply mode.
  • Server-initiated workspace/applyEdit requests also mutate files through applyWorkspaceEdit().
• Network
  • None directly; communication is local stdio JSON-RPC to subprocesses.
• Subprocesses / native bindings
  • Spawns language servers with ptree.spawn().
  • Workspace diagnostics spawns cargo, npx, go, or pyright.
  • BiomeClient and SwiftLintClient spawn CLI tools.
  • Optional lspmux detection spawns lspmux status; supported servers may be wrapped through lspmux client.
• Session state (transcript, memory, jobs, checkpoints, registries)
  • Caches config per cwd in configCache.
  • Caches LSP clients per command:cwd, with pendingRequests, diagnostics, openFiles, serverCapabilities, and project-load state.
  • Caches custom linter clients by serverName:cwd.
  • Updates client lastActivity; optional idle-timeout cleanup is driven by setIdleTimeout().
• Background work / cancellation
  • Every request has an abortable timeout signal.
  • Aborting an in-flight LSP request sends $/cancelRequest.
  • Background message readers persist for each live client until process exit/shutdown.

Limits & Caps

• Tool timeout clamp: default 20, min 5, max 60 seconds — TOOL_TIMEOUTS.lsp in packages/coding-agent/src/tools/tool-timeouts.ts.
• LSP request default timeout inside sendRequest(): 30_000ms — DEFAULT_REQUEST_TIMEOUT_MS in packages/coding-agent/src/lsp/client.ts.
• Warmup initialize timeout default: 5_000ms — WARMUP_TIMEOUT_MS in packages/coding-agent/src/lsp/client.ts.
• Project-load wait fallback: 15_000ms — PROJECT_LOAD_TIMEOUT_MS in packages/coding-agent/src/lsp/client.ts.
• Idle-client sweep interval when enabled: 60_000ms — IDLE_CHECK_INTERVAL_MS in packages/coding-agent/src/lsp/client.ts.
• Diagnostic message output cap: first 50 messages — DIAGNOSTIC_MESSAGE_LIMIT in packages/coding-agent/src/lsp/index.ts.
• Single-file diagnostics wait: 3_000ms — SINGLE_DIAGNOSTICS_WAIT_TIMEOUT_MS.
• Batch/glob diagnostics wait per file: 400ms — BATCH_DIAGNOSTICS_WAIT_TIMEOUT_MS.
• Glob diagnostic target cap: first 20 matches — MAX_GLOB_DIAGNOSTIC_TARGETS.
• Workspace symbol cap: first 200 entries — WORKSPACE_SYMBOL_LIMIT.
• Reference context cap: first 50 references include source context — REFERENCE_CONTEXT_LIMIT.
• References retry count: 2 retries, 250ms backoff — REFERENCES_RETRY_COUNT, REFERENCES_RETRY_DELAY_MS.
• Directory rename cap: 1_000 file pairs — MAX_RENAME_PAIRS.
• detectLspmux() state cache TTL: 5 * 60 * 1000ms; liveness check timeout: 1_000ms — STATE_CACHE_TTL_MS, LIVENESS_TIMEOUT_MS in packages/coding-agent/src/lsp/lspmux.ts.
• Workspace diagnostics output cap: first 50 lines from the subprocess.

Errors

• Missing or invalid inputs are usually returned as text with details.success: false, not thrown:
  • missing file/query/new_name
  • invalid JSON in payload
  • no matching server
  • invalid rename_file source/destination conditions
• resolveSymbolColumn() throws explicit errors for missing files, missing symbols, and out-of-bounds #N selectors; these surface as LSP error: ... or request-specific error text.
• sendRequest() rejects on timeout with LSP request <method> timed out after <ms>ms.
• Client process exit rejects all pending requests with an exit-code/stderr error assembled in getOrCreateClient().
• Single-file action failures inside the main try become LSP error: <message>.
• request has its own error envelope: LSP error from <server> on <method>: <message>.
• Some server failures are intentionally softened:
  • diagnostics continue when one server fails
  • rename_file suppresses workspace/willRenameFiles “method not found” errors and records other server errors as notes
  • code_actions ignores codeAction/resolve failures and applies unresolved actions when possible
• Caller aborts are not converted to text: ToolAbortError is rethrown. A wall-clock tool timeout without a caller abort instead throws ToolError: LSP <action> timed out after <N>s on <server>. ....

Notes

• status reports configured servers from LspConfig and labels each one via getActiveClients(): (configured, not started) means the binary resolves on PATH but no request has spawned it; a live client reports its status.
• getLspServerForFile() excludes createClient adapters and linter-only servers; navigation/refactor actions never target Biome/SwiftLint custom clients.
• getServersForFile() matches both file extensions and exact basenames from fileTypes; config can target names like Dockerfile if present.
• symbol matching is exact first, then case-insensitive, and falls back to the Nth occurrence on the specified line only; it never scans other lines.
• For definition, references, and rename against project-aware servers, omitting symbol while passing line is rejected with a ToolError instead of silently falling back to the first non-whitespace column.
• code_actions uses query in two different ways: server-side context.only filter in list mode, client-side title/index selector in apply mode.
• rename and rename_file default to apply. Preview requires apply: false.
• request with file: "*" is treated the same as omitted file: it does not build workspace-specific params.
• reload does not recreate a client immediately after killing it; the next request triggers reinitialization.
• workspace/applyEdit can apply edits initiated by the server outside the direct tool action result path.
• detectLspmux() can be disabled with PI_DISABLE_LSPMUX=1; only rust-analyzer is in DEFAULT_SUPPORTED_SERVERS.
• Startup LSP discovery (discoverStartupLspServers(cwd) in sdk.ts) runs for enableLsp && options.hasUI; the background warmup additionally requires !settings.get("lsp.lazy"). lsp.lazy defaults to true, so by default discovered servers are surfaced with status "available" (gray dot in the welcome screen) and cold-start through getOrCreateClient() on first use (lsp tool call or edit/write on a matching file type). Print/RPC/ACP/script sessions skip discovery and warmup entirely. See docs/sdk.md § Startup performance.
• configCache is per-process and never auto-invalidated; config changes require a fresh process to be observed by getConfig() callers.