XERJ
XERJ: the search engine for AI agents. A new way for AI to search for data: one local Rust binary that indexes your code, docs, specs and logs, plus Corpus Hub packs, and returns cited answers.
Local-first search engine and MCP server for AI agents. One Rust binary indexes code, docs,logs, JSONL/CSV and PDFs for BM25 full-text, vector and hybrid search, code search and agentmemory, behind an Elasticsearch-compatible API. Works with Claude Code, Cursor and any MCP client.
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XERJ is a community-trusted local AI search that indexes any folder automatically, so yourcoding agent stops burning tokens reading files one by one and pulls the exact code itneeds instead. Reference coding is its main use case and the clearest win: point an agentat a task and it downloads the open-source repos closest to it, indexes them, and reuseshow they solved the problem before writing its own code. In a controlled study that cut acoding agent's output tokens by 2.7x at the same 16/16 solve rate(case study), and people reportroughly 5x in everyday work(field reports).It is enough for a smaller, cheaper model to out-code a pricier one working from memory,while you spend less time in fix loops. Try it now with a one-prompt install:
Install XERJ (docs: https://xerj.org/llms.txt), index this project's sources, and set up
reference coding: clone and index the open-source repos closest to what we're building,
and search how they solved a problem before writing code.
Or run it yourself:
curl -fsSL https://xerj.org/get | sh
xerj --insecure --data-dir ~/xerj-data &
xerj init # wire XERJ into Claude Code/Cursor (MCP + skill), one command
xerj autoindex ~/my-project
xerj search "how do we rotate the WAL segment" # ranked passages, file:line
xerj def "euler_to_rotationmatrix" # go-to-definition: file:line + signature
xerj gain # what it did for you — counted, not estimated
For several IDs or questions at once, use xerj batch-search --input queries.jsonor MCP xerj_batch_search: ordered results, citations and per-item errors.
Keep that data directory outside any folder you will autoindex. data/ is not in thebuilt-in ignore list, so --data-dir ./data inside a tree you then index makes the nodeindex its own storage.
At startup, Data dir shows the resolved absolute path, Data source identifiesthe flag, selected config file or default, and Data status says whether thislaunch created the directory. A new directory can make an older node's indicesor owner account appear missing: restart with the previous --data-dir or--config. XERJ does not discover or migrate other data directories automatically.
Windows and a hand-verified install are under Install by hand.
That --insecure flag is a trust boundary, not a formality. It turns off TLS and API-keyauth, so every caller that can reach the port is a superuser who can read and delete everyindex, including every /_memory namespace. It is meant for one user on a dev machine: afresh node binds 127.0.0.1 only, and a cleartext bind on any other interface refuses tostart unless you explicitly allow it. The full model is indocs/SECURITY_MODEL.md.
Join the community
You join XERJ by running it and sending back one short field report on what it was like: asingle commit or PR. That report is the membership card, and it is the only thing theproject asks in return for a free, Apache-2.0 binary. It is what keeps the engine improvingfor whoever runs it next.
Humans and AI agents are both welcome; this is deliberately not an agents-only project.Whether you indexed a repo over lunch or an agent installed XERJ mid-session in someoneelse's codebase, the ask is the same: one short report saying what you pointed it at, whatyou used it for, and your honest verdict. A negative verdict is a good report. If somethingbroke, that is a separate issue or fix on top.
Field-report PRs are CLA-exempt, so they merge without a signature. The path that works onany build is a plain gh pr create adding exactly one markdown file underuser-feedback/16-agent-field-reports/, withnothing else in the diff. On a build that has it, xerj feedback drafts the report andfills in version, OS and what was indexed, and xerj feedback --open-pr opens the PR foryou. Check xerj --help for whether your binary has the command.
The measured reason: reference coding
An agent that greps pulls whole files into its context, up to 1.06M input tokens on onecorpus in our measurements, and still has to read them. An agent that queries XERJ gets thepassage. Measured end to end on code the model had not memorised(case study: 8 tasks, 4 languages,16 runs per arm, real claude -p token counts):
| output tokens | cost | solved | |
|---|---|---|---|
| from memory only | 260,916 | $11.18 | 11/16 |
| grep-driven agent | 26,477 | $3.27 | 16/16 |
| XERJ | 9,982 | $1.58 | 16/16 |
That is 2.7x fewer output tokens than grep and 26x fewer than memory alone at the same solverate, and up to 278x fewer on a single Java task. In real development, users report roughly5x fewer tokens end to end(field reports).The value is gated by memorisation: it wins on private, internal, niche or post-cutoff code,and is neutral to harmful on popular public libraries the model already knows. The honestlimits are in the case study.
Feed it any folder
Reference coding is one use of the same primitive: xerj autoindex <folder> makes an agentknow a corpus instead of grepping it. One command indexes code, docs, logs, PDFs, SQLite andawkward CSVs into typed, queryable indices for search, RAG, security audits and agentmemory, with no schema to write and no pipeline to configure.
xerj --insecure --data-dir ~/xerj-data & # start it
xerj autoindex ~/my-project # point it at anything
--insecure again means no TLS and no auth — every caller a superuser — so this is thesame one-user-on-a-dev-machine boundary as above (security model).
XERJ sniffs every file, works out what it is, and creates one index per dataset it finds.Code arrives with its symbols and line numbers through tree-sitter, not as flat text:
phase A: 593 datasets inferred, 1955 junk/skipped files
phase B: indexing 25329 files with 8 workers
done in 158.1s, 593 datasets, 83103 records live, 790 junk records
Share an offline data map with xerj autoindex map --prefix myproject --html xerj-map.html --redact-paths, or use --md xerj-map.md for Markdown. Reportsinclude dataset counts, symbol names, graph hubs when available, skipped-fileinformation and suggested searches. Review metadata names before sharing.Examples, privacy scope and reproduction.
What people point it at
- Reference coding: index the OSS projects nearest your problem and retrieve how they solvedit before writing code (the measured use case above).
- Codebase Q&A and RAG: index a repo, ask for the mechanism, get the passage with
file:lineinstead of a directory listing. - Security audits: index a target tree and query for sink patterns, secrets and dangerouscalls across every file type at once.
- Log and incident analysis: mixed formats become typed indices with the aggregations youwould expect from Elasticsearch.
- Agent long-term memory:
/_memory/{namespace}stores what an agent learns and recalls itby meaning next session.
How the prompt works
llms.txt gives your agent the ordered steps: install, start theserver, xerj autoindex ., query with any Elasticsearch client, and the reference-codingloop (clone similar OSS, index it, retrieve the mechanism before writing, cite what you use,respect licenses).
The reason it helps: an agent working from memory retry-loops on any API it has notmemorised, and grep only tells it where to look; the recovery is still reading source intocontext, up to 1.06M input tokens on one corpus in our measurements. An agent that queriesXERJ reads the exact passage instead. The 2.7x fewer output tokens than grep (26x vs memoryalone, 2.1x cheaper) at the same 16/16 solve rate is inThe measured reason above, with a companion runscoring 9/9 with retrieval versus 0/9 from memory on a Rust library the model had never seen.
More prompts that work on a fresh install:
- "Read https://xerj.org/llms.txt, set XERJ up as your search backend, index
./docs, andshow me one example query per index it created." - "Run
xerj autoindex mapand tell me what is in this data (types, counts and the gotchasit recorded), then answer my questions with search instead of reading files." - "Use XERJ's
/_memory/notesAPI as your long-term memory for this project: store what youlearn as you work, and recall it by meaning next session."
Worked, validated examples for each capability: xerj.org/docs/recipes.
Boot, bulk ingest, search, vector kNN, live dashboards, no cuts.Watch it on xerj.org ortry the live playground.
Install by hand
curl -fsSL https://xerj.org/get | sh
Windows PowerShell:
irm https://xerj.org/get.ps1 | iex
Nix (builds from source; nix develop opens a shell with the Rust toolchain):
nix run github:xerj-org/xerj -- --version
One static binary, no JVM, no dependencies. Prebuilt for Linux, macOS and Windows on x86-64and arm64. The x86-64 builds target x86-64-v2 (SSE4.2: Intel Nehalem 2008 and later, AMDBulldozer and later) and use AVX2 and FMA at runtime when the CPU has them, so a pre-Haswellmachine runs the same binary. It speaks the Elasticsearch API, so existingclients, dashboards and tooling work against it unchanged.
First commands after install (the installer prints where xerj landed; add it to your PATHif needed): xerj --insecure --data-dir ~/xerj-data &, wait until http://localhost:9200responds, then xerj autoindex ~/my-project. See Index a folder.
For a host with no runtime internet access, follow theair-gapped deployment recipe. The default lexicalembedder is offline; neural mode needs the three model files staged locally before the firstsemantic operation.
Index a folder
Start the server, then point autoindex at anything:
xerj --insecure --data-dir ~/xerj-data & # local dev: no TLS, no auth
xerj autoindex ~/my-project
That is the dev-machine trust boundary from the top of this README — no TLS, no auth, everycaller a superuser. It is fine on a laptop because a fresh node binds 127.0.0.1 andnothing else; a shared host wants the auth-on start just below.
If your server has auth on, which is the default for every start without --insecure(including any start from a config file), hand autoindex the same key. It never picks thekey up from xerj.toml; pass --api-key or set XERJ_API_KEY, or every request comes back401 Unauthorized:
xerj --data-dir ~/xerj-data & # auth on: key minted on first boot
export XERJ_API_KEY="$(cat ~/xerj-data/admin.key)" # <data_dir>/admin.key
xerj autoindex ~/my-project
That is the whole setup. There is no schema to write and no pipeline to configure. XERJsniffs each file, works out what it is, and creates one index per dataset it finds:
phase A: 593 datasets inferred, 1955 junk/skipped files
phase B: indexing 25329 files with 8 workers
done in 158.1s, 593 datasets, 83103 records live, 790 junk records
Source files go through tree-sitter, so code arrives with its symbols and line numbersinstead of as flat text. CSV, JSON, JSONL, XML, YAML, SQLite, PDF, DOCX, PowerPoint(.pptx, one record per slide), Excel (.xlsx, one dataset per sheet), EPUB books (one record per chapter), Jupyter notebooks(one record per heading section, any kernel), man pages (roff, one record per section), HTML, mail (.eml and mbox mailboxes,including a Google Takeout export) and common log formats are all handled. Unity projects get first-class treatment: text-serialized scenes,prefabs and assets become one record per GameObject/Component, .meta files become aGUID-to-path table, and MonoBehaviour records carry script_class/script_path so "whichscenes use this script?" is a single query (binary-serialized assets need Force Text to bereadable; generated dirs like Library/ are auto-skipped and recorded).
Search it
This is the Elasticsearch API, so you already know this part:
# what did it find?
curl localhost:9200/_cat/indices
# full-text
curl "localhost:9200/ax-*/_search?q=checkout+error"
# structured
curl localhost:9200/ax-orders/_search -H 'content-type: application/json' -d '{
"query": { "range": { "total": { "gte": 100 } } },
"aggs": { "by_status": { "terms": { "field": "status" } } }
}'
Vector and hybrid search use the same knn and semantic syntax you would send toElasticsearch. Any Elasticsearch client library works if you point it at localhost:9200.
Score results with Jev
A search score tells you which result is above which, but not whether a result really answersyour question. Jev, a servicefrom TypeSafe AI, does that: give it a question and a document and it returns a number from 0to 1, how well the document answers. XERJ works with it in two ways.
1. Reorder your results with Jev (optional). Add "rerank": {} to a _search and XERJ sendsthe top results to Jev, then sorts them by the numbers it gets back. On the public FiQA test,result quality goes from 0.24 to 0.36 (nDCG@10), for about $0.64 in total for 648 searches.Treat the numbers as a way to sort, not as exact percentages: they are not well calibrated.This sends the text of those results to TypeSafe's servers. It stays off until you set akey, and [rerank] enabled = false forbids it completely. Readdocs/RERANK.md before turning it on.
2. Get the same kind of answer locally. POST /v1/systemone and POST /_decide accept thesame questions in the same format, but XERJ answers them itself, by looking up the most similardocuments you have already labelled (for example messages already marked spam or not spam).Nothing leaves your machine and no key is needed. It only works if you have labelled examples;on AG News (120k labelled examples) it picks the right label 92% of the time. The officialjev-reranker Python client works against a XERJ node without changes(test). XERJ answers under its own name, xerj-history-vote-1;it is not Jev.
Measurements and how to reproduce them:benchmarks/beir-hybrid andbenchmarks/decisions-as-retrieval.
Connect an agent over MCP
Not every agent can run a shell command. Desktop assistants and function-calling hosts reachtools through the Model Context Protocol, and the binary you just installed is the MCPserver. There is nothing else to download and nothing to compile:
xerj --insecure --data-dir ~/xerj-data & # 1. the node the tools query
xerj mcp # 2. MCP stdio server (your client runs this)
xerj mcp speaks MCP over stdio and proxies to the node named by XERJ_URL (defaulthttp://localhost:9200). It does not start a node; step 1 is the prerequisite. The MCPserver adds no trust of its own — it is the same binary talking stdio to your client andplain HTTP to the node, so the node's boundary is the one that counts, and step 1 aboveboots the same --insecure dev node. Drop this into your MCP client's config:
{
"mcpServers": {
"xerj": {
"command": "/home/you/.local/bin/xerj",
"args": ["mcp"],
"env": { "XERJ_URL": "http://localhost:9200" }
}
}
}
Use an absolute path. The sh installer (Linux, macOS, and Windows Git Bash, MSYS and Cygwin) puts xerj in ~/.local/bin (xerj.exe on Windows; command -v xerj confirms) and does not edit PATH. The PowerShell installer (get.ps1) puts xerj.exe in %LOCALAPPDATA%\Programs\xerj and adds that directory to the user PATH ((Get-Command xerj).Source confirms; XERJ_NO_PATH=1 opts out). MCP hosts launched from a desktop icon do not inherit yourshell's PATH. If the node is running with auth (anything but --insecure), add"XERJ_AUTH": "ApiKey <key>" alongside XERJ_URL; the key is in <data-dir>/admin.key.
Supported agents
Twenty-six clients can register xerj mcp as a local stdio server. The entry is always the sametwo fields - the absolute path to the binary, and mcp as its only argument - but where that entrylives and which key wraps it differ per client. tested means the server was registered in thatclient and xerj_search appeared in its tool list; untested means the path and shape aretranscribed from the client's own documentation and nobody has run it yet. Six rows have been run.OpenCode v2.1.2 on Windows against xerj v1.0.0-rc.97 answered initialize and tools/listwith its full tool list. Cline CLI 3.0.73 on Linux against xerj v1.0.0-rc.98 loaded thissection's mcpServers block at ~/.cline/data/settings/cline_mcp_settings.json. xerj_searchappeared in the tool list Cline handed the model (named xerj__xerj_search) among that binary's20 tools, and Cline executed one xerj_search call. The model turn was a local OpenAI-compatiblestub, because no provider key was available; the MCP server was the real xerj mcp process. TheIDE's MCP Servers > Configure button was not part of that run. Kimi Code CLI 2.3.1 and the Kimidesktop app on Linux against xerj v1.0.0-rc.99 (built from source) loaded this section'smcpServers block at ~/.kimi-code/mcp.json: the client spawned xerj mcp as a child processwith the env block intact (verified through /proc/<pid>/environ), and xerj_search appearedin the tool list. Claude Code 2.1.311 on Kali Linux against xerj v1.0.0-rc.100 registeredxerj mcp with claude mcp add in the local, project and user scopes; xerj_search appeared in/mcp among that binary's 22 tools, and Claude Code executed one xerj_search and one xerj_defcall against an autoindexed repository. DeepSeek Harness 44.7.0 on Windows againstxerj v1.0.0-rc.99 loaded this row's - insert: block from a profile patch at$DSH_HOME/profiles/desktop/cordis.patch.yml: in the contributor's run, the harnessspawned xerj mcp without an application restart, exposed mcp__xerj__xerj_search,and executed a search. The tested entry was the profile patch; the dsh/ bundlewas not exercised. The run set XERJ_DISABLE_FEEDBACK=true and observed no automaticfield report. Contributor's verification and limits. Antigravity on Windows 11 (x86_64-pc-windows-msvc) against xerj v1.0.0-rc.100 loaded this section's mcpServers block at ~/.gemini/config/mcp_config.json with XERJ_DISABLE_FEEDBACK=true: the client spawned xerj.exe mcp, received 22 tools in tools/list (including xerj_search and xerj_def), and executed one xerj_search and one xerj_def call against an autoindexed repository (iscvlab/mcp-bridges).
Correcting an untested row is a welcome first PR.
| Client | Config file | Key | Note | Tested |
|---|---|---|---|---|
| OpenCode | opencode.json in the project, or ~/.config/opencode/opencode.json |
mcp.servers |
one command array, environment not env, needs a project root |
tested |
| Claude Code | .mcp.json (project scope) or ~/.claude.json (local scope, the default, or user scope); claude mcp add writes any of them |
mcpServers |
-- before the command is recommended; xerj mcp also registers without it |
tested |
| Cursor | .cursor/mcp.json in the project, or ~/.cursor/mcp.json |
mcpServers |
no type for stdio |
untested |
| Codex | ~/.codex/config.toml, or .codex/config.toml in trusted projects |
[mcp_servers.xerj] |
TOML, not JSON | untested |
| Gemini CLI | .gemini/settings.json or ~/.gemini/settings.json |
mcpServers |
gemini trust the folder or stdio shows Disconnected |
untested |
| GitHub Copilot in VS Code | .vscode/mcp.json |
servers |
needs "type": "stdio"; the portable .mcp.json uses mcpServers |
untested |
| Windsurf | %APPDATA%\devin\mcp_config.json, ~/.config/devin/mcp_config.json |
mcpServers |
the path is Devin's now, not ~/.codeium/windsurf |
untested |
| Claude Desktop | %APPDATA%\Claude\claude_desktop_config.json, ~/Library/Application Support/Claude/claude_desktop_config.json, ~/.config/Claude/claude_desktop_config.json |
mcpServers |
quit the app fully, not just the window | untested |
| Cline | ~/.cline/data/settings/cline_mcp_settings.json (CLI); the IDE opens it from MCP Servers > Configure |
mcpServers |
disabled and autoApprove are Cline-specific; the CLI run did not need them |
tested |
| Roo Code | .roo/mcp.json in the project, or <VS Code User>/globalStorage/rooveterinaryinc.roo-cline/settings/mcp_settings.json |
mcpServers |
the project entry wins on name clashes | untested |
| Kilo Code | kilo.jsonc or .kilo/kilo.jsonc in the project, ~/.config/kilo/kilo.jsonc global |
mcp |
one command array, like OpenCode | untested |
| Continue | ~/.continue/config.yaml, or any file in .continue/mcpServers/ |
mcpServers |
a YAML list, not a map; Agent mode only | untested |
| Zed | ~/.config/zed/settings.json (on Windows, run zed: open settings file) |
context_servers |
the key is not mcpServers |
untested |
| JetBrains AI Assistant | settings UI only: Settings > Tools > AI Assistant > Model Context Protocol | mcpServers |
a separate store from Junie | untested |
| Junie | .junie/mcp/mcp.json in the project, ~/.junie/mcp/mcp.json user |
mcpServers |
older posts omit the mcp/ folder |
untested |
| Amp | ~/.config/amp/settings.json, .amp/settings.json in the workspace, or amp mcp add |
amp.mcpServers |
the key keeps the amp. prefix |
untested |
| Goose | ~/.config/goose/config.yaml, %APPDATA%\Block\goose\config\config.yaml |
extensions |
cmd, not command, and YAML |
untested |
| Kiro | .kiro/settings/mcp.json in the workspace, ~/.kiro/settings/mcp.json user |
mcpServers |
${VAR} expansion needs approval |
untested |
| Antigravity | ~/.gemini/config/mcp_config.json, or .agents/mcp_config.json in the workspace |
mcpServers |
remote servers use serverUrl |
tested |
| OpenClaw | ~/.openclaw/openclaw.json (JSON5) |
mcp.servers |
transport: "stdio" |
untested |
| DeepSeek Harness (dsh) | $DSH_HOME/cordis.patch.yml, or a profile patch |
- insert: with @deepseek-ai/dsh-mcp-client |
one plugin instance per server | tested |
| Warp | Settings > Agents > MCP servers, or ~/.warp/.mcp.json and .warp/.mcp.json in the project |
mcpServers |
working_directory, not cwd |
untested |
| Augment Code | ~/.augment/settings.json for the Auggie CLI; the IDE uses its own panel |
mcpServers |
that file does not drive the IDE | untested |
| Qwen Code | ~/.qwen/settings.json, or .qwen/settings.json in the project |
mcpServers |
mcp.allowed can silently hide it |
untested |
| Kimi CLI | ~/.kimi-code/mcp.json, or .kimi-code/mcp.json in the project |
mcpServers |
the current Kimi Code CLI, not the archived ~/.kimi/mcp.json |
tested |
| Grok CLI | ~/.grok/config.toml, or .grok/config.toml in the project |
[mcp_servers.xerj] |
Grok Bot has no local stdio registration | untested |
Codex and the Grok CLI read TOML, so the entry is a table:
[mcp_servers.xerj]
command = "/abs/path/to/xerj"
args = ["mcp"]
OpenCode and Kilo Code take one command array, and Kilo uses the same shape one level shallower:
{"mcp": {"servers": {"xerj": {"type": "local", "command": ["/abs/path/to/xerj", "mcp"], "environment": {"XERJ_URL": "http://localhost:9200"}}}}
{"mcp": {"xerj": {"type": "local", "command": ["/abs/path/to/xerj", "mcp"]}}}
Continue and Goose read YAML:
# ~/.continue/config.yaml
mcpServers:
- name: xerj
command: /abs/path/to/xerj
args:
- mcp
# ~/.config/goose/config.yaml
extensions:
xerj:
type: stdio
cmd: /abs/path/to/xerj
args:
- mcp
enabled: true
Amp keeps the key namespaced, VS Code and Copilot need servers plus a transport, Zed calls themcontext servers, and OpenClaw nests them under mcp:
{"amp.mcpServers": {"xerj": {"command": "/abs/path/to/xerj", "args": ["mcp"]}}}
{"servers": {"xerj": {"type": "stdio", "command": "/abs/path/to/xerj", "args": ["mcp"]}}}
{"context_servers": {"xerj": {"command": "/abs/path/to/xerj", "args": ["mcp"], "env": {}}}}
{mcp: {servers: {xerj: {command: "/abs/path/to/xerj", args: ["mcp"], transport: "stdio"}}}}
DeepSeek Harness loads one MCP server as one plugin in $DSH_HOME/cordis.patch.yml, or in a profile patch at $DSH_HOME/profiles/<profile>/cordis.patch.yml. The same block is the profile bundle in dsh/, and its command is xerj on PATH. If that file is only [], replace the array with the block below; appending under [] is not valid YAML. env and cwd are optional stdio fields (args defaults to [], env to {}, cwd to ""). When the node is not running --insecure, add XERJ_AUTH: "ApiKey <key>" under env:
# $DSH_HOME/cordis.patch.yml
- insert:
- id: mcp-xerj
name: '@deepseek-ai/dsh-mcp-client'
config:
serverName: xerj
transport: stdio
command: xerj
args:
- mcp
env:
XERJ_URL: "http://localhost:9200"
cwd: ""
Three candidates from the original list are deliberately absent. Aider has no MCP client support atall (Aider-AI/aider#3314 is still open). T3 Code isthe other direction: it hosts an MCP endpoint other agents connect to, and its sessions inherittheir servers from the harness underneath. Grok Bot has no documented local stdio registration; theGrok CLI does, which is the grok row above.
Twenty-three tools are exposed when Hub tools are enabled. Eleven are thin proxies over an endpoint XERJ already serves:
| Tool | What it does |
|---|---|
xerj_search |
keyword search over an index, from plain words (query) or an ES query-DSL clause (query_dsl) |
xerj_semantic_search |
recall by meaning over a semantic_text field, the query embedded server-side (default embedder is lexical feature-hashing, not neural, unless the node runs --embed-mode neural) |
xerj_vector_search |
kNN over a dense_vector field |
xerj_hybrid_search |
RRF or linear fusion of sub-queries |
xerj_memory_store / xerj_memory_recall |
durable agent memory in a namespace, recalled by text, meaning or vector |
xerj_brain_overview / xerj_brain_ego / xerj_brain_link / xerj_brain_unlink |
the second-brain link index: orient, expand one node's evidence-backed neighborhood, assert and retire links |
xerj_plan |
a plain-words filter in, validated query DSL out (POST /_ask; deterministic and rule-based, not an LLM) |
For xerj_search, pass {"prefix":"project","query":"retry policy"} to searchproject-*, matching xerj search --prefix project. prefix is resolved bythe same function as the CLI: the prefix xerj autoindex --prefix stores, soMy_Proj searches my-proj-*. Use index for an explicit index name orpattern instead; non-empty index and prefix cannot be combined. An emptyprefix, a prefix with no [a-z0-9] character, or a prefix that cannot name anindex is an error. With neither argument, the tool searches ax-*.
For new callers, query is a plain string and structured ES query-DSL goes inquery_dsl — {"index":"docs","query_dsl":{"match_all":{}}}. Do not combineboth fields. The published schema separates the types to simplify tool calls(#2549); it cannot guarantee a model emits valid JSON. Existing callers maystill pass an object in query, and omitting both fields retains match_allbrowsing. Prefer an explicit query_dsl clause when browsing is intended.
Search tools and xerj batch-search default to an 8,000 UAX #29 word budgetwhen max_tokens is omitted or null. A larger integer requests more evidence;accounting explains any trimming. This is not a byte cap or a model/BPE tokenlimit. Errors and mandatory xerj_search staleness hints are outside thisbudget and remain visible.
xerj_def finds local definitions with the same query, ranking and location deduplicationas xerj def --json. For example, {"symbol":"Cache","prefix":"project","kind":"struct","lang":"rust","k":5}searches project-*; index can replace prefix, with the same scope rules as xerj_search.symbol also accepts capability phrases. k must be 1–50 (default 5); optional max_tokenscaps the response. Results are ES JSON: declarations live in hits.hits[]._source.code,locations in ax_path/path and line/start_line; older file hits may use fields._passage.hits.total counts engine matches before deduplication. No match returns an empty hit list.As in the CLI, kind/language filters are ignored when no target index maps the fieldor any target index maps it as numeric. Ranking is lexical. This tool queries the configured node;xerj_hub_def instead looks up definitions in a named Hub pack.
Two more are not plain proxies: xerj_map returns the per-index field map from the autoindexcatalog (trimmed to a byte cap, otherwise verbatim), and xerj_code_search runs the xerj codereference-coding pipeline (tools/xerj-code/) and returns its rendered text.xerj_index_budget counts a folder and estimates its index against the node's disk budgetbefore xerj autoindex hashes anything (it does not index). xerj_autoindex_remove dropsone autoindexed folder after listing it, and deletes nothing unless confirm is true.xerj_status probes the node banner, cluster health and visible indices withup to three bounded reads. A missing autoindex catalog does not mean the nodehas no data; refused or malformed probes remain errors or unknown status.xerj_batch_search retrieves ordered batches with per-item outcomes and citations.xerj_corpus_feedback rates a hub corpus.xerj_field_report files a field report, and xerj_hub_find, xerj_hub_def and xerj_hub_askanswer from Corpus Hub packs already on the machine (the xerj ask flow).
xerj mcp --help prints the same config block and the full option list. The machine-readabletool schemas are published atxerj.org/docs/agents/schemas/mcp-tools.json,generated from a live tools/list, never hand-written, and gated in CI(scripts/mcp-schema-check.sh) plus a unit test, so the published list cannot drift from theserved one.
Why it exists
Agents burn their context window reading files. The PHP in WordPress core is about 5.2million tokens, or 26 full context windows, so an agent cannot simply read it. Grep does notsolve this either, because a grep hit is a line, and judging that line means opening thewhole file.
Querying an index costs kilobytes per question instead. Inan AI security audit of WordPress core,an agent worked across 1,492 PHP files on roughly 26,000 tokens, which is what it takes toload about half a percent of the tree.
Use cases
- Reference coding: your coding agentretrieves how peer projects already solved it instead of re-deriving. Measured 2.7x feweroutput tokens than grep-driven coding (26x vs memory alone); users report ~5x in realdevelopment.
- Code search and security audits:AST-aware indexing, so an agent finds a function instead of a line.
- AI search and RAG: full-text, vectorand hybrid retrieval in one query, with no separate vector database.
- Agent memory: durable recall with aknowledge graph over your own documents.
- Log analytics and observability:logs, metrics and traces in one engine.
- Elasticsearch replacement:same wire protocol, one binary.
Runnable examples live in recipes/ and docs/examples/.
Elasticsearch compatibility
XERJ implements the Elasticsearch REST API: indices, documents, bulk, search, aggregations,mappings, kNN, scroll, reindex and the _cat endpoints. Kibana and the official clientlibraries connect to it directly. One boundary worth knowing before you point export toolingat it: scroll is a bounded up-front snapshot, not a segment-walking cursor, so a query whoseexact total exceeds the snapshot window is refused with a 400 rather than silentlytruncated. Use search_after for result sets of any size(the cap).
The conformance suite runs on every commit and currently passes 1444 of 1454 cases (0 failed, 10 skipped). It livesin engine/tests/es-compat-yaml, and the remaining gaps arelisted there rather than hidden. XERJ is compatible with the API. It is not areimplementation of Elasticsearch internals, and it is not a fork.
Benchmarks
XERJ is benchmarked head to head against Elasticsearch 8.13.4 across ingest, full-textsearch, aggregations, vector search, and reads issued under a concurrent write flood. Thelatest closed-loop run scores 55 wins, 26 ties, 4 losses, including 1.72x ingest throughputand a 1.61x smaller on-disk footprint.
All four losses are the same gap: read p99 while a high-rate writer runs. It iswritten up in full ratherthan left out. Results, methodology and the harness are atxerj.org/benchmarks and indemo/playbooks, so you can rerun them yourself. Treat any number youcannot reproduce with skepticism, including ours.
Code indexing
Source files are parsed with tree-sitter and indexed AST-aware — symbols plus full text — so anagent retrieves a function, not a line. On an Apache Lucene checkout (6,113 source files, 51 MB)single-threaded in-process extraction runs at ~1,500 files/s (13 MB/s); the tree-sitterparse is ~72% of that and is the per-file floor. Reproduce it with:
XERJ_EXTRACT_BENCH=/path/to/repo cargo test -p xerj-autoindex --release \
extract_bench -- --nocapture --ignored
Re-indexing is incremental: a file whose content is byte-identical to the last indexedgeneration skips the parse entirely and carries its committed result forward, so a re-run afterediting a handful of files does work proportional to what changed, not to the whole repo — thecommon edit-and-rerun / CI case, typically over 95% unchanged. The full content hash still runsto detect changes, so total re-index time is floored by hashing, not parsing.
Build from source
You need a stable Rust toolchain.
git clone https://github.com/xerj-org/xerj
cd xerj/engine
cargo build --release -p xerj-server
./target/release/xerj --insecure --data-dir ~/xerj-data
The x86-64 release builds target x86-64-v2 (SSE4.2; set per target inengine/.cargo/config.toml). The HNSW dot-product kernel also compiles an AVX2+FMAvariant and selects it at runtime when the CPU has both features. RUSTFLAGS overridesthat file, so a local build can opt into the host CPU:
RUSTFLAGS="-C target-cpu=native" cargo build --release -p xerj-server
To run the conformance suite against a running server:
cargo run --release -p es-yaml-runner -- --dir tests/es-compat-yaml/yaml
Documentation
- Guides and API reference
- Recipes for common tasks
- Roadmap: what ships today versus what is coming, verified against therelease binary. Release-by-release view:milestones; live status:project board; standing pointer:pinned roadmap issue
- Changelog
Reference pages for individual subsystems, written against the source and including thelimits each one does not lift:
- Second brain for the relationship layer over indexed documents:the
/_graphroutes, evidence on links, the eight detectors and the two-hop cap. - Console reader for the console's corpus home, the reader forany record (an email with its attachments, a PDF page) and read-only guest mode, withthe rendering rules that keep a hostile document inert and what it does not render.
- Scripting for the Painless subset, where scripts run, and theresource limits that bound them.
- Snapshot and restore for the supported subset of thesnapshot API, and what restore replaces.
- Sharing for
xerj share: read-only guest access to one indexedfolder through a link and a passcode, what a guest can and cannot reach, and the threatmodel. - Security model for authentication, the reserved
.xerj-memory-*namespace, API keys and what is not enforced. - Reranking for the optional
reranksearch stage: an external judgereorders the top hits by a calibrated probability. It is the only search-time featurethat sends document text off the node (proxy embeddings and the WAL tap also send textwhen an operator configures them; the page lists every outbound connection a node canopen), it needs an operator-configured provider key, andits ranking quality with the real model is not verified. - XERJ vs Lucene 10.3.1 for a source-pinned, six-axis comparisonof their storage and search designs.
Contributing
Pull requests are welcome from humans and AI agents alike; seeJoin the community above. The baseline contribution is one short fieldreport: a plain gh pr create adding one markdown file underuser-feedback/16-agent-field-reports/.Field-report-only PRs are CLA-exempt, so they merge without a signature.
For code changes, see CONTRIBUTING.md for the workflow andCLA.md for the contributor licence agreement, which is one signature percontributor rather than one per pull request. Agents opening a PR should state that an agentwrote it and follow AGENTS.md /.github/AI_CONTRIBUTIONS.md.
Bugs and feature requests go to GitHub issues.
License
Apache 2.0.