FreqBlog Music Metadata
Server Details
Audio features (BPM, key, mood, genre) for real tracks - a Spotify audio-features replacement.
- Status
- Healthy
- Last Tested
- Transport
- Streamable HTTP
- URL
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Tool Definition Quality
Average 4.7/5 across 6 of 6 tools scored.
Each tool has a clearly distinct purpose: music theory key compatibility, BPM search, key search, single track audio features, batch audio features, and catalog text search. No overlapping or ambiguous tools.
All tool names follow a consistent verb_noun pattern in snake_case (e.g., find_compatible_keys, get_audio_features_batch), making the naming predictable and easy to understand.
With 6 tools, the server is well-scoped for a music metadata service. Each tool provides essential functionality without redundancy or unnecessary complexity.
The tool set covers the core domain comprehensively: search, key compatibility, BPM/key filtering, and audio features for both single and batch queries. No obvious gaps for the intended use case of music discovery and analysis.
Available Tools
6 toolsfind_compatible_keysFind Harmonically Compatible KeysARead-onlyInspect
Given a Camelot key (e.g. "8A", "12B"), return the harmonically compatible keys for DJ
mixing — the same key, the relative major/minor, and the adjacent +/-1 keys on the
Camelot wheel. With extended=true also returns the +7/-7 energy-boost / energy-drop
keys. Pure music theory — no catalog lookup and no quota cost. Pair with find_tracks_by_key
to then pull actual tracks in each compatible key.
| Name | Required | Description | Default |
|---|---|---|---|
| camelot | Yes | Camelot key, e.g. '8A' or '12B'. | |
| extended | No | Also return the +7/-7 energy-boost / energy-drop keys. |
Output Schema
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already provide readOnlyHint=true and openWorldHint=false, indicating safe, deterministic behavior. Description adds no contradiction and reinforces with 'pure music theory — no catalog lookup and no quota cost', providing extra context beyond annotations.
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?
Three concise sentences: first explains basic functionality, second covers the extended option, third provides nature and guidance. No extraneous information, well-structured and front-loaded with key action.
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 low complexity, full schema coverage, annotations, and an output schema, the description completes the picture by explaining the DJ mixing context and the Camelot wheel logic. No gaps remain.
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 descriptions for both parameters. The description does not add parameter-level details beyond the schema, but it provides useful context for the extended parameter's effect (energy-boost/drop keys), which adds value beyond the schema description.
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 it returns harmonically compatible keys for DJ mixing given a Camelot key. It distinguishes from siblings by noting it's pure music theory with no catalog lookup, and suggests pairing with find_tracks_by_key.
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 tells when to use: for Camelot key compatibility analysis. States it's no catalog lookup and no quota cost, and recommends pairing with find_tracks_by_key to get actual tracks. This contrasts with sibling tools that likely involve catalog searching.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
find_tracks_by_bpmFind Tracks by BPMARead-onlyInspect
Find catalog tracks near a target tempo. Returns tracks whose BPM is within
+/-tolerance of bpm, ordered by closeness then popularity — useful for DJ set
planning, workout playlists, or tempo-matching. Each returned track carries full audio
features. To also constrain by musical key, combine with find_tracks_by_key.
| Name | Required | Description | Default |
|---|---|---|---|
| bpm | Yes | Target tempo in BPM. | |
| limit | No | Max tracks (default 10). | |
| tolerance | No | Plus/minus BPM window (default 2). |
Output Schema
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations (readOnlyHint: true), the description adds that results are ordered by closeness then popularity and that each track carries full audio features. It does not contradict annotations and provides useful behavioral context.
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 three sentences, front-loaded with the core purpose, and every sentence contributes meaning without redundancy or unnecessary detail.
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 3 simple parameters and an output schema exists, the description fully covers purpose, usage, ordering, and combination with related tools, leaving no gaps for an AI agent to select and invoke correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
With 100% schema coverage, the description explains how bpm, tolerance, and limit interact: 'within +/-`tolerance` of `bpm`' adds meaning beyond individual descriptions. However, the schema already describes parameters well, so the description adds moderate 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 clearly states 'Find catalog tracks near a target tempo,' specifying the verb 'find' and resource 'catalog tracks.' It provides context about BPM tolerance, ordering by closeness and popularity, and use cases like DJ planning or tempo-matching, effectively distinguishing it from sibling tools like find_tracks_by_key.
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 mentions when to use the tool ('useful for DJ set planning, workout playlists, or tempo-matching') and suggests combining with find_tracks_by_key for key constraints, offering clear guidelines and alternatives.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
find_tracks_by_keyFind Tracks by Musical KeyARead-onlyInspect
Find catalog tracks in a given musical key — for harmonic mixing and key-locked
playlists. key accepts Camelot ("8A"), Open Key ("1m"), or a key name ("A-Minor",
"F#-Major"). Returns tracks ordered by popularity, each with full audio features. To
discover which keys mix well with a given key first, use find_compatible_keys.
| Name | Required | Description | Default |
|---|---|---|---|
| key | Yes | Camelot ('8A'), Open Key ('1m'), or key name ('A-Minor', 'F#-Major'). | |
| limit | No | Max tracks (default 10). |
Output Schema
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate readOnly and openWorld, and description adds that results are ordered by popularity with full audio features. No contradiction with annotations.
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 efficient sentences front-load purpose and key formats, then output ordering and sibling reference. No superfluous content.
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 tool's low complexity, full annotations, and presence of output schema, the description covers purpose, usage, key formats, output behavior, and sibling relation adequately.
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%, providing descriptions for both parameters. The description reinforces key formats but adds no new parameter semantics beyond the schema, warranting baseline score 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 finds catalog tracks by musical key for harmonic mixing and key-locked playlists. It distinguishes from sibling find_compatible_keys by specifying this tool directly finds tracks by key.
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?
It explicitly says to use find_compatible_keys first to discover which keys mix well, providing clear guidance on when to use this tool vs alternatives.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
get_audio_featuresGet Audio FeaturesARead-onlyInspect
Get audio features for ONE track — BPM, musical key (name + Camelot + Open Key), energy, danceability, valence, acousticness, instrumentalness, liveness, speechiness, loudness, mood, mood_vector, genre, time signature, duration and more.
This is the drop-in replacement for Spotify's deprecated /audio-features endpoint.
Provide EXACTLY ONE identifier:
- `track` (optionally with `artist`) — e.g. track="Blinding Lights", artist="The Weeknd".
- `isrc` — e.g. "USUM71900001".
- `mbid` — a MusicBrainz recording UUID.
- `spotify_id` — a Spotify track ID, URI, or URL.
Returns a JSON object of features. Some feature fields may be null for tracks resolved
via the fallback catalogs (only audio-derived values are present for fully analysed
tracks). If a track name is not yet in the catalog, the API queues an on-demand
analysis and this tool reports that it is queued — retry in ~30s-2min. If you only
have a fuzzy or partial name, call search_catalog first to find the exact track.| Name | Required | Description | Default |
|---|---|---|---|
| isrc | No | ISRC, e.g. 'USUM71900001'. | |
| mbid | No | MusicBrainz recording ID (UUID). The precise key when there is no ISRC, e.g. pre-1986 recordings. | |
| track | No | Track title. Use with `artist` when known. Required field is ONE of track/isrc/mbid/spotify_id. | |
| artist | No | Artist name. Only used with `track`; required when the title is <=2 characters. | |
| spotify_id | No | Spotify track ID, 'spotify:track:...' URI, or open.spotify.com URL. |
Output Schema
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds significant behavioral context beyond the annotations, such as the on-demand analysis queuing and retry timing, and potential null fields for fallback tracks. It aligns with readOnlyHint and openWorldHint without contradiction.
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 well-structured with front-loaded output details, then usage instructions, then caveats. It is reasonably concise, though the first few sentences could be slightly tightened for efficiency.
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 presence of an output schema, the description covers all necessary contextual aspects: identifier options, fallback behavior, queuing, and when to search first. It is fully adequate for correct tool invocation by an AI agent.
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?
All parameters have schema descriptions (100% coverage), and the description adds crucial context: exactly one identifier required, track optionally with artist, and artist required for short titles. This clarifies usage beyond the schema alone.
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 it gets audio features for one track, listing specific features like BPM, musical key, etc. It distinguishes itself from siblings by explicitly stating it's for a single track, contrasting with batch and search 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 provides clear guidance on when to use this tool, including the required identifier types and when to use search_catalog for fuzzy names. It implicitly excludes batch use by stating 'ONE track', but could be more explicit about not using for multiple tracks.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
get_audio_features_batchGet Audio Features (Batch)ARead-onlyInspect
Get audio features for MANY tracks in one call (up to 50) — ideal for analysing a whole playlist at once. Pass a list of {track, artist?} objects.
Returns counts (`found` / `not_found`) plus a per-track `results` array, where each
entry's `result` is the same feature object as get_audio_features (or null when not
found). Each track consumes one quota unit. For a single track, use get_audio_features.| Name | Required | Description | Default |
|---|---|---|---|
| tracks | Yes | List of {track, artist?} objects to look up (max 50). |
Output Schema
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and openWorldHint=true. The description adds useful behavioral detail: output structure (counts, results array with per-track feature object or null) and quota unit consumption. 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?
Two efficiently-written sentences plus a quota note. No extraneous words; key information is front-loaded and easy to parse.
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 existence of an output schema (referenced), the description sufficiently covers return values, quota, and differentiation from siblings. It provides all necessary context for correct tool invocation.
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% and the description adds little beyond restating the parameter structure (list of {track, artist?} objects) and max 50 limit. It reinforces but does not significantly extend schema meaning.
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 it gets audio features for many tracks (up to 50) in one call, contrasting with the single-track sibling get_audio_features. The verb 'get' and resource 'audio features for many tracks' is specific and unambiguous.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly states ideal for analyzing a whole playlist and directs to use get_audio_features for a single track. Also mentions quota consumption, providing clear when-to-use and 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.
search_catalogSearch Music CatalogARead-onlyInspect
Full-text search the catalog by any mix of track / artist / album tokens. Use this to resolve a fuzzy, partial, or misspelled name into concrete tracks BEFORE calling get_audio_features.
Returns lightweight stubs (itunes_track_id, track_name, artist_name, album, etc.) ranked
by relevance — NOT audio features. Take the best match's track_name + artist_name and
pass them to get_audio_features, or reuse its itunes_track_id as a `track_id` seed for
discovery tools.| Name | Required | Description | Default |
|---|---|---|---|
| q | Yes | Search query — any mix of artist / track / album tokens. | |
| limit | No | Max results (default 10). |
Output Schema
| Name | Required | Description |
|---|---|---|
No output parameters | ||
Tool Definition Quality
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds behavioral context beyond annotations: it returns stubs ranked by relevance, not audio features. Annotations already declare readOnlyHint and openWorldHint, so the description complements them. Missing details like pagination or sorting, but overall sufficient.
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 concise, consisting of three sentences. The first sentence immediately states the action (search). The second sentence gives usage context. The third sentence details return type and next steps. No wasted words, highly efficient.
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 presence of an output schema, the description provides complete context: explains what the tool does, when to use it, what it returns, and how to proceed. It effectively covers the tool's role in a workflow without omitting critical information.
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 already describes both parameters (q and limit) with high coverage (100%). The tool description does not add new parameter information beyond repeating the schema's description for q. Therefore, it adds minimal value, meeting the baseline score 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 it performs full-text search on a music catalog by track, artist, or album tokens. It distinguishes itself from siblings by explicitly contrasting with get_audio_features and mentioning that it returns lightweight stubs, not audio features.
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 instructs when to use: 'Use this to resolve a fuzzy, partial, or misspelled name into concrete tracks BEFORE calling get_audio_features.' It also provides clear next steps and alternatives, such as passing the result to get_audio_features or reusing the itunes_track_id.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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